Last year's outbreak of severe acute respiratory syndrome (SARS) provided the World Health Organization (WHO) an opportunity to show the world its teeth. Newly installed director-general Jong-Wook Lee intends to use them to take a bite out of the world's costliest diseases.

In recent months, Lee has sounded a clarion call for the WHO to lead a scale-up of AIDS treatment and other targets spanning a wide spectrum—from eradicating polio to curbing tobacco use, combating cardiovascular disease, and significantly reducing childhood mortality.

But the WHO's new stances on SARS and HIV/AIDS have by far received the most attention. The organization has updated guidelines for AIDS treatment and redoubled its commitment to providing antiretroviral therapy to 3 million people (of the 6 million who need it) worldwide by 2005—a $5.5 billion initiative.

The rapid emergence and spread of SARS stirred something of a crisis mentality. Through its Global Outbreak Alert and Response Network, the WHO—under former director-general Gro Harlem Brundtland—responded by deploying epidemiologists and other experts throughout the world. The experts pieced together their findings in Geneva during daily teleconferences, resulting in the eventual identification of the mysterious coronavirus.

More controversial were the advisories against travel to Toronto, Hong Kong and parts of China, providing an unprecedented illustration of the WHO's singular discretion.

“I didn't realize until later that that was the first time [travel advisories had ever been issued],” says Ray Arthur, associate director for global health at the US National Center for Infectious Diseases. “If you look at it from the perspective of what measures needed to be taken, it's not a surprise,” he adds.

The WHO is now trying to draw on the clout it gained during the SARS epidemic to foster similar urgency in battles against HIV/AIDS and other long-entrenched enemies.

“We looked very hard at the SARS example and we realized that you can do this and you can survive it and have a very real impact,” says Jim Yong Kim, an advisor to Lee in Geneva. Previous recommendations for AIDS treatment took years to adopt and prescribed dozens of protocols—such as CD4 counts and the measurement of viral loads—that made treatment prohibitive to a large part of the world, Kim says.

In a matter of just months, the organization developed new guidelines incorporating models such as Haiti's HIV Equity Initiative. “Up to now,” Kim says, “what we have done has been much too complicated and much too slow.”

Lee's tenure has been marked by such emphasis on activist, ground-level goals, but his biggest challenges, say some observers, could lie in galvanizing the member states.

“I don't think [the WHO] has the resources yet to manage that,” says epidemiologist Ernest Drucker of Montefiore Medical Center in New York. The WHO remains dependent on its member states to commit material, financial and ideological backing. Channeling diverse, and occasionally competing, agendas, Drucker says, is often a tall order.

Others point to a heightened sensitivity to international health. “Any time there's a major epidemic, obviously it attracts a lot of attention from the public,” says Arthur. “You perform well when you're under the spotlight, and that's recognized; you don't perform well, and there are probably some consequences.”

This material is part of Nature Medicine's 10 year anniversary series. For more content related to these special focus issues, please see