Zhang is a fifth-year chemistry graduate student at the University of Wisconsin at Madison. He is hardworking, popular with his colleagues, and should be on the threshold of a rewarding future in science. Yet a 2002 visit to Zhang's native China nearly derailed that career. He is so scarred by the experience that he agreed to be interviewed only on condition that his real name was not used in this article.

Nature's reporters are used to Chinese scientists requesting anonymity before speaking openly on controversial issues. But Zhang is not worried about the attitude of the government in Beijing. Rather, he is wary of consular officers, FBI operatives and other officials of the US federal government who seem to regard him as a potential terrorist, rather than a valuable member of their country's scientific workforce.

Fighting back: security clamp-downs on foreign researchers and students have sparked widespread protests at US universities. Credit: M HUMPHRIES

Zhang's nightmare began in January 2002, when he left Madison to spend the Chinese New Year with his friends and family. Zhang knew that immigration controls had been tightened up since the terrorist attacks of the previous September, and sought advice from his university about how to avoid any problems getting back into the United States. He carried with him proof of enrolment, details of the courses he had taken, a letter from his department and government forms confirming his immigration status — which he assumed would allow him to get his student visa renewed. “I did all that I could have done,” Zhang says.

But when he went to the nearest US consulate for an interview, Zhang was told he would have to wait. His particular field of study overlapped with a 'watch list' of technologies of potential interest to terrorists that had been supplied to consular officials. This meant that his application would have to undergo an interagency security review, involving security officials from agencies including the FBI and the Department of State.

Days stretched into weeks, then months, with no news of progress with his application. Eventually, Zhang found himself working in the office of a shipping company to make ends meet, while his colleagues continued their research without him. Because he didn't know when he was going to return, he was forced to continue paying rent on his apartment in Madison. Zhang finally received his visa in September 2002, leaving him hopelessly behind with his PhD studies. “My whole plan for graduation has been postponed,” he says.

People who were thinking about coming to the United States for graduate school are now thinking twice

Zhang is not an anomaly. “There have been enormous problems,” says John Wright, who chairs the University of Wisconsin's chemistry department. Most of the students and postdocs whose applications to enter the United States have been questioned have eventually been let in. But Wright frets that the new immigration rules will deter future applications, weakening his department, which is currently considered among the best in the world. “The quality of research will decrease,” he says.

Many US researchers and university officials share Wright's concerns. The United States is a nation of immigrants, and nowhere is this more evident than in the country's research labs. Strip away the legions of foreign PhD students, postdocs and tenure-track researchers, and the behemoth that is the US scientific enterprise would look much less impressive (see figure). What's more, in recent years, other countries have realized the value of attracting the best of the world's young researchers, and have started taking steps to compete more effectively in this marketplace (see 'You're welcome').

So will the United States' draconian response to the terrorist threat cause a fundamental shift in the international movement of researchers — and perhaps even alter the global balance of scientific power? It's difficult to say, because attaching firm numbers to such trends is all but impossible. Scientists travel to the United States on a wide variety of visa types, depending on the purpose and length of their stay. And because they make up a tiny proportion of the total number of foreigners entering the country each year, even a major decline would fail to show up in overall visa statistics. Data collected in different countries are also hard to compare: many nations don't separate visiting scientists from researchers in the humanities and other disciplines; some consider students separately from postdoctoral researchers, whereas others lump them all together.

“One of the great problems in dealing with this issue is that you get tons of anecdotes, but it is difficult to get data,” says Norman Neureiter, who served as science adviser to US Secretary of State Colin Powell for three years until September 2003. Nature's enquiries reinforce Neureiter's view of the anecdotal evidence. Our reporters found dozens of examples of scientists at every level who have experienced problems entering the United States. And in some cases, they found researchers now looking for work in countries such as Australia, Britain and Canada, rather than enduring the US immigration process.

Out in the cold

The sketchy data available suggest that such anecdotes illustrate a widespread problem — and that this is particularly acute for postdoctoral researchers in the 'hard' sciences and engineering. In November, for instance, the Association of International Educators, an organization based in Washington DC that promotes scholarly exchange worldwide, released a survey of more than 300 US colleges and universities. The survey revealed that the number of students whose start dates were delayed by visa problems was 48% higher in 2003 than at the start of the previous academic year; for 'scholars' — a broad category dominated by young postdoctoral researchers — the increase was 76%. More than three-quarters of the delayed students were in the physical sciences, biological sciences or engineering; among the scholars, these disciplines accounted for 93% of those who experienced significant delays.

Other surveys paint a similarly bleak picture. Last July, the American Institute of Physics reported that nearly a quarter of foreign students who applied to study towards a PhD in physics in the United States in 2002 were initially denied a visa. The number of foreign researchers working at the five largest institutes on the National Institutes of Health campus in Bethesda, Maryland, declined in 2003 for the first time in the nine years over which records have been kept. Most strikingly, the total number of visiting scholars in the United States declined in the 2002–03 academic year for the first time in almost a decade.

There's a perception that visas are too difficult to get and the United States is an unwelcome place - Victor Johnson

For some observers, these statistics are enough to set off alarm bells about the future health of US science. “We're at a critical juncture now, and I think everybody senses it,” says Irving Lerch, director of international affairs with the American Physical Society in College Park, Maryland. Although the likely consequences of the visa delays remain a matter of debate, their main cause is clear — new security procedures introduced following the terrorist attacks of 11 September 2001.

In the immediate aftermath of those events, the state department began expanding its 'Technology Alert List', designed to prevent dangerous technologies getting into the hands of terrorists or hostile states. It is now classified, but a version issued in August 2002 contained roughly 150 items, including such broad labels as 'microbiology', and common pieces of lab equipment such as low-energy lasers. So if you work on, say, infectious disease, or use relatively innocuous devices that have found their way onto the state department's list, your application to enter the United States is likely to be referred to the FBI and other federal agencies for a security review.

Singled out

Scientists from China have borne the brunt of the new policy — even though its nationals have never been implicated in terrorism against US targets. The survey by the Association of International Educators, for instance, found that more than a third of all visiting students whose entry to the United States was delayed were from China. In part, the large number of Chinese who have been affected by the new restrictions reflects the fact that they make up the biggest single group of foreign scientists seeking employment or education in the United States. But some Chinese researchers, who point out that the current US administration was pursuing an aggressive policy towards their country even before the 2001 terror attacks, believe that they are being singled out for harsh treatment (see 'We are not the enemy').

Meanwhile, for researchers from countries such as Iran, and several others in the Middle East, security reviews have become an almost insurmountable barrier (see 'Never apply for a US visa again!' ). Because the US government sees Iran as a sponsor of terrorism, its scientists cannot enter the United States without undergoing an interagency review. Even senior Iranian officials with longstanding ties to the US scientific community have been unable to attend major conferences. “I have had many invitations, but I had to say no,” says Reza Mansouri, a physicist and the deputy of research at the Iranian Ministry of Science, Research and Technology in Tehran.

You can't go to a large international scientific meeting without visas being the issue on everyone's mind. I think there's going to be a solidarity movement against the United States - Wendy White

Scientists from other countries need not face a full security review, even if their work appears on the state department's watch list. But a memo sent in August 2002 along with a revised version of the list ensnared many scientists who expected to sail through the immigration process. The paper instructed that, “when in doubt”, consular officers should send applications to the state department's headquarters in Washington DC. As the consular staff involved were mostly inexperienced, they were in doubt all too often. The resulting backlogs caused delays of up to a year.

The memo is still causing problems. The state department claims that more than 80% of cases referred to Washington are dealt with in 30 days. But Wendy White, who directs the Board on International Scientific Organizations at the US National Academies, disputes this figure. “For the scientists we hear from, the average wait time is still over five months,” she says.

Delays were exacerbated last July by a new rule requiring virtually all visa applicants to be interviewed face-to-face by a consular officer. Most scientists were already being pulled into US embassies for interviews, but they suddenly found themselves part of a much longer queue. When Thomas Brunold, an assistant professor in chemistry at the University of Wisconsin, went home to Switzerland for a short visit last June, he had to wait for three months to get an interview to renew his US visa. “I told them I had a research group of nine people to run,” Brunold says. But his pleas fell on deaf ears, and the resulting delay cost Brunold a month's salary.

For many researchers, the most frustrating thing about the new immigration requirements is their inconsistency. As a result, some visa applications shoot through the system whereas others are held up for months. And when this happens, there is usually no explanation. “The transparency in the process is completely missing,” says Olexei Motrunich, a Ukranian physicist who has worked in the United States since 1994, but has been stranded in his home country since July, unable to take up a postdoctoral position at the University of California, Santa Barbara.

“I have been telling my relatives and friends how great America is; how one does not feel foreign in this country,” says Motrunich. “Now I have to explain to the same people why, after more than eight years of doing science in the United States, I have a hard time receiving a visa to continue my work.”

Number one no more

For some visiting scientists, the problems don't end at the US border. Catheryn Cotten, who directs the International Office at Duke University in Durham, North Carolina, says that foreign nationals are finding it more difficult than ever to secure social-security numbers, driver's licences and other essential documents. Mansouri adds that press reports of assaults against Iranian students at US universities are causing many of his country's young scientists to think instead about studying in Britain or Australia.

Such comments are worrying organizations that strive to promote international scholarly exchange. “There's a perception that visas are too difficult to get and the United States is an unwelcoming place,” says Victor Johnson, associate executive director for public policy at the Association of International Educators.

Not surprisingly, researchers and university administrators in other countries who are recruiting from the pool of scientists now experiencing problems entering the United States are quietly satisfied with the turn of events. Countries such as Australia, Britain and Canada were already increasing their intake of foreign students before US visa restrictions were imposed — and this trend has accelerated since then.

I can understand that Americans are worried about their security, but I don't understand why people like me are a threat to their security

Perhaps even more significant is the calibre of the students and researchers now considering destinations other than the United States. “I've had professors tell me that the quality of the Iranian students is phenomenal,” says Amy Aldous, graduate-studies recruitment manager at the University of Waterloo in Ontario, Canada. Baowen Li, a theoretical physicist at the National University of Singapore, says that he is now seeing many more applications from China's élite universities. “The change is not in quantity but quality,” says Li. “We have benefited a lot from the US policy.”

But is this the start of a trend that could ultimately undermine the United States' leadership in science? Andreas Schleicher, who heads the Indicators and Analysis Division at the Organisation for Economic Co-operation and Development in Paris, argues that US dominance is so overwhelming that this is unlikely. “More than a quarter of all students studying abroad still travel to the United States,” he says. But Neureiter, who has wrestled with the issues from inside the US administration, is not so sanguine. “I tend towards an apocalyptic view,” he says.

How things unfold will depend on whether the visa delays experienced by visiting scientists represent teething troubles or a more lasting obstacle. State-department officials argue that they are now taking steps to improve the situation. New rules should let students jump to the front of the interview line so that they do not miss their start dates. And by March, a new computer system should connect embassies overseas directly to security agencies in the United States. The idea is to speed the interagency security reviews, preventing cases such as Motrunich's from getting stuck in limbo.

Still, the ongoing focus on security means it will be impossible to handle applications as quickly as they were dealt with before 2001. “I think the best we can do is to try to keep with our goal of processing all of the cases within a 30-day period,” says Janice Jacobs, deputy assistant secretary of consular affairs at the state department.

Some US universities report that things do now seem to be getting back on track: at Duke, for instance, the number of foreign students studying the sciences rose once more in 2003, after two years of zero growth. But Neureiter is worried about the potential impact of a rule implemented last week that requires the fingerprinting of all visa applicants, and of another that will soon demand that students and visiting scholars pay a non-refundable fee of $100. “You can't go to a large international scientific meeting without visas being the issue on everyone's mind,” agrees White. “I think there's going to be a solidarity movement against the United States.”

Back in Madison, Zhang is now applying for postdoctoral positions, while writing up his PhD thesis. Despite his experiences, he says that he would rather stay in the United States, where he knows the research community. “But people who were thinking about coming here for graduate school are thinking twice,” he warns. While Zhang was in China working at the shipping company, he befriended his boss's family. The executive's two daughters were thinking of studying medicine. Last year, they began their courses in Britain.

Written and reported by Geoff Brumfiel, with David Cyranoski, Carina Dennis, Jim Giles, Hannah Hoag and Quirin Schiermeier.