There can't be many coffee-break conversations as tense as some of those that take place in Gershon Golomb's lab at the Hebrew University of Jerusalem. Golomb, who heads a research group working on improved methods of drug delivery, lives in Efrat, an Israeli settlement in the occupied territory of the West Bank. To Palestinians, the very existence of such towns is a major barrier to peace. Golomb is also a senior officer in the Israeli reserve forces, and until recently served in the army for up to two months every year, often on the West Bank. All of this makes it surprising — and unique, claims Golomb — that one of his team is a Palestinian.

That researcher, Yousef Najajreh, lives in Beit Jala, just a few kilometres from Efrat. Even nearer to Najajreh's hometown lies the Israeli settlement of Gilo — to which Irith Gati, the group's technician, returns home each evening. When violence flares overnight — as it frequently does — the group's discussions the next morning are understandably strained. “There can be shooting between Gilo and Beit Jala,” says Najajreh, whose house has been hit by stray bullets. “I come in and we accuse each other's community of starting it. But at the end of the day we are there for the science.”

To those who believe that scientific collaboration can help break down the barriers raised by conflict, the fact that Najajreh and his Israeli colleagues are able to work together against the common enemy of disease is an encouraging sign. And although few working relationships are overshadowed quite so starkly by the conflict as those in Golomb's lab, examples of joint Israeli–Palestinian research projects are not hard to find — a paper in this issue of Nature, for instance, on the seismology of the Dead Sea region, boasts both Israeli and Palestinian contributors (see page 497).

But it would be naive to conclude that such collaborations tell a simple story of scientists successfully putting their political differences aside in the pursuit of knowledge. Researchers from both communities are able, in many cases, to manage their huge divergences in viewpoint — but these differences cannot simply be disregarded. Would you expect an Israeli academic who has lost a friend in a suicide bombing to have no misgiving about working alongside people from a society that sees the perpetrator as a martyr? And is it any surprise to learn that Palestinian researchers who are shut out of their labs by the Israeli army, and whose neighbours' homes have been bulldozed, may view the idea of collaborating with Israeli scientists with incredulity?

For an outsider, even finding the right language to discuss the situation is problematic. When e-mailing scientists to set up meetings before my visit to the region, I inadvertently offend one Palestinian researcher by asking about “science on the West Bank”. He requests, politely but firmly, that I refer to the territories occupied by Israel as “Palestine”. But for many Israelis, his preferred label for this disputed land is equally inflammatory.

In the end, Israeli and Palestinian scientists alike ignore my clumsy attempts to find acceptable terminology. They are happy to discuss their work, and how it has been affected by the conflict — or, in rare cases, defined by it (see 'Know the enemy'). I visit in August, a period of relative calm. Hamas and other militant Palestinian groups have called a ceasefire, and the Israeli army's presence in the occupied territories is more low-key than in the preceding months. As a result, I am able to venture onto the West Bank to meet Palestinian scientists without encountering too many problems. In Israel, students are on their summer break and there is a relaxed atmosphere on the modern, Western-style campuses.

Yet within two days of my departure, the violence and despair have returned. Today, the outlook is as bleak as anyone can remember. Suicide bombings have resumed, bringing terror to the heart of Israeli society, and Israel's military has embarked on a vigorous security clampdown, leading to the deaths of around 40 Palestinians. One Israeli minister has even aired the possibility of assassinating Yasser Arafat, president of the Palestinian National Authority.

Such hardline attitudes find few echoes among Israel's academics. Like their counterparts in many other countries, their political views tend mainly towards the liberal end of the spectrum. Many researchers criticize their government's strategy in the occupied territories, and argue that politicians should do more to push the peace process forward. What's more, Israeli academics are generally enthusiastic about the idea of working with Palestinian scientists. “A lot of Israelis hate the idea of sitting in an ivory tower and doing nothing,” says Benjamin Geiger, a cell biologist at the Weizmann Institute of Science in Rehovot. “Over the past few years there have been many, many attempts to create interactions with Palestinian colleagues.”

Some of these attempts have failed because of the huge disparity in resources at the disposal of these neighbouring research communities. Israel is a world leader in fields such as biotechnology and physics, and the country's labs are as well-equipped as those anywhere in the world. By contrast, the total amount spent on research across all of the Palestinian universities is a fraction of that deployed by a single major Israeli research institution. Sometimes, Israeli scientists who are interested in reaching out to Palestinian colleagues simply fail to find a partner.

But numerous collaborations do exist, spanning fields from chemistry to plant biology. The Israeli researchers involved stress the scientific value of these efforts, but many are also motivated by a desire to promote peace by helping their Palestinian colleagues to build up their research capacity. “We know that building science communities is important,” says microbiologist Hervé Bercovier, vice-president for research at the Hebrew University, which has been particularly active in promoting joint projects with Palestinian institutes.

In some fields, the results of collaborative projects will feed directly into any peace negotiations. Some of the region's key aquifers lie beneath the West Bank, and hydrologists frequently find themselves involved in political arguments about how these resources should be distributed (see 'Water and the wall'). “If we want to share water in a professional manner, we need to work together,” says Gedeon Dagan, a geophysicist at Tel Aviv University who sits on the steering committee for a project on the hydrology of the Jordan Valley involving both Israeli and Palestinian scientists.

Talk to Palestinian researchers about the value of joint projects with Israeli scientists, however, and you hear a diverse set of opinions. The Palestinian Ministry of Higher Education opposes links with Israeli institutions. And although many Palestinian researchers ignore this official line, many of those who work in towns that have borne the brunt of security operations by the Israeli army support their government's view.

At An-Najah National University in the West Bank town of Nablus, chemist Maher An-Natsheh explains why his experience of the conflict has left him unwilling to work with Israeli scientists. “We are in a state of war,” he says. “They have to give Palestinians the right to exist; then we can start talking about collaborations.”

An-Najah University's students often vote for militant groups such as Hamas in campus elections, and the university is regarded as a nest of terrorists by the Israeli authorities — the army says that several suicide bombers have been An-Najah students.

Two months before my visit, Fadi Alawneh, a journalism student at An-Najah, tried to avoid Israeli army checkpoints by crossing a deep ditch; he lost his balance when approached by an armoured vehicle and died from his injuries. He was the thirty-fifth An-Najah student to die since the present Palestinian uprising, or intifada, began in September 2000, says An-Natsheh.

During this period, An-Najah University has been closed several times. An-Natsheh, who is the university's vice-president for academic affairs, says that deliveries of chemicals are frequently impounded on suspicion that they may be used to make explosives. In Hebron, some 80 kilometres away, where tensions are particularly high due to the presence of a small Israeli settlement surrounded by a hostile Palestinian community, it is a similar story (see 'A campus under siege', page 449).

West Bank towns are also frequently held under curfew. Research at many institutions ceases during such clampdowns, but some scientists take risks to continue their work. In July 2002, for instance, a curfew order prevented staff at the Applied Research Institute-Jerusalem, which conducts environmental studies, from commuting to and from their headquarters in Bethlehem. Rather than stop working, they moved computers and equipment to the houses of friends and family in Beit Jala, where the narrow streets made it easier to evade the Israeli army. “You could easily knock on a door and hide if you saw a patrol,” says Jad Isaac, the institute's general director.

Even against this background, some Palestinians are open to the idea of interacting with Israeli scientists. But they are not always comfortable about expressing this view in public, for fear of attracting a backlash from their own community. Last month, for example, a small group of Palestinians attended a 'Frontiers of Science' conference in Istanbul, Turkey, which was organized by the US National Academy of Sciences with the aim of promoting dialogue between researchers from across the Middle East. But some of these researchers were anxious about the signals that they were sending out by attending. “We don't want the media to take pictures and announce that Palestinians met Israelis,” says Awni Khatib, a chemist at Hebron University.

Other Palestinian researchers are simply so frustrated with the difficulties of daily life that they have no wish to work with scientists from the country they see as the cause of their troubles. Even if researchers from Nablus and Hebron did want to collaborate with Israeli scientists, they would struggle to travel to the nearest Israeli universities in Jerusalem, just a few dozen kilometres away. The journey would require a special permit, which can take months to arrive and still does not guarantee access.

Travelling back to Jerusalem from Hebron one afternoon, the reality of this situation is brought home. The taxi-van in which I'm travelling is stopped at a checkpoint and instructed to turn back — the road has been closed for security reasons. Nearing the end of a hot and uncomfortable journey, our driver has other ideas. He initially withdraws as requested, but quickly cuts back onto the main road and speeds past the checkpoint, escaping the young soldier's attention. “Don't worry, he would have shot our tyres before aiming at us,” another passenger says.

Not all Palestinians face such severe restrictions on their movements, however. And where security controls are less stringent, attitudes towards working with Israelis are much more positive. At Al-Quds University in Abu-Dis, a suburb of eastern Jerusalem, Palestinian researchers are building links with nearby Israeli universities, with encouraging results. “Before we started collaborating in 1994, Al-Quds spent US$35,000 a year on research,” says Ziad Abdeen, who works on nutrition and disease and is the university's dean of research and graduate studies. “Now it is $3 million.”

Most of this money has come from abroad, and much of it was made available specifically to promote joint projects with Israeli institutions. The increased funding, says Abdeen, has provided new facilities such as the university's molecular-biology lab, constructed using money from the Belgian government for a joint project with the Hebrew University. Israeli academics have also helped researchers at Al-Quds to gain experience in writing grant proposals. “Our research culture was created by working with our Israeli colleagues,” says Abdeen.

The issue of collaborative projects is not the only one to split the Palestinian research community. In April 2002, more than 100 academics, mostly Europeans, wrote to the British newspaper The Guardian, calling for the European Union to suspend Israel's participation in its Framework research programme, in protest at “the violent repression of the Palestinian people”. The idea of boycotting Israeli science was rebuffed by the EU, but generated a remarkable amount of debate. Isolated incidents of academics refusing to work with Israeli colleagues were reported, and the controversy was re-ignited in June this year, when a pathologist at the University of Oxford, UK, was suspended from his post after rejecting an application from a prospective PhD student who had served in the Israeli army (see Nature 424, 120; 200310.1038/424120a).

Many Palestinian researchers reject the idea of boycotting Israeli science. “It's counter-productive,” says Abdeen. Even among Palestinians who support the idea of an economic boycott on Israel, there is unease about the idea of extending protests into the scientific arena. In towns such as Nablus and Hebron, however, some researchers support the actions of those foreign academics who have refused to work with Israeli scientists. Despite his own willingness to work with Israelis if the collaboration strengthens Palestinian science, Khatib is among their number. “Pressure must be exerted on Israel,” he says. “I support the boycott because it can enhance movements in this direction.”

Such comments are distressing to Israeli academics, especially those involved in collaborations with Palestinians. There is a saying in Israel that reflects the country's love of debate: “put two Israelis in a room, and you'll get three opinions”. But this definitely does not apply to discussions about the call for a scientific boycott. “You're not going to get three opinions on that,” says Jonathan Gressel, a plant biologist at the Weizmann institute. “I don't think it ever helps to keep scientists out of science for political reasons.” His colleague Geiger agrees: “This breaks with one of the most cherished and important features of science: that it is international and non-political.”

Scientific bodies and publications, including Nature (417, 1; 2002)10.1038/417001a, have spoken out against the idea of boycotting Israeli science, and an anti-boycott petition has attracted more than 15,000 signatures. The academics behind the letter to The Guardian have also since stressed that any boycott should not extend to Israelis who work on joint projects with Palestinian researchers.

Nevertheless, many Israeli scientists feel that the debate has had a chilling effect on their relations with colleagues abroad. When I suggest to Shy Arkin, a biochemist at the Hebrew University, that the boycott is only weakly supported in Britain, he immediately dissents: “It's not a small minority.”

“You hear of a variety of initiatives,” agrees Geiger. “Some are individual people expressing their views; others are channelled in a more institutional way.” Geiger points out that the European Molecular Biology Organization has come under pressure from some academics to suspend the membership of Israeli scientists.

Other Israeli academics tell of more personal attacks. “There is an unpleasant feeling in Europe,” says Michael Beenstock, an economist at the Hebrew University. Just back from a meeting in Finland, Beenstock recounts an argument with an academic who began to berate him about his government's policies towards the Palestinians, after reading the institutional affiliation on his name badge. “He very quickly became critical of 'you Israelis',” says Beenstock. “I lost my temper until someone told us both to shut up.”

It is understandable that Beenstock might lose his cool under such circumstances — his office is less than 100 metres from the site of last summer's attack on a Hebrew University cafeteria, in which nine people were killed by a bomb placed by Palestinian construction workers (see 'Touched by terror'). For those who have been exposed to such acts of violence, being blamed for the conflict is hard to bear.

Back in their drug-delivery research lab, Golomb and Najajreh try not to engage in similar arguments, as they know that they can never agree over the conflict. Yet somehow they manage to work together. “We turn down the volume on our arguments because we have a shared value against sickness,” says Najajreh.

Until the political leaders of Golomb's and Najajreh's respective communities can negotiate a peace agreement that both sides can accept, however, this shared value will remain bound by a tenuous thread.