WHAT MONEY CAN BUY.

Each May, representatives from the hundred and ninety-two member nations of the World Health Organization travel to Geneva to set policies for the coming year. The assembly lasts a week, and the delegates often find themselves devoting as much of that time to politics as they do to matters of life or death. This year, on the opening day, Elena Salgado, the assembly's president, spoke bluntly about the growing chasm between the "rich world," where people live in health and comfort, and everywhere else. The mortality rate for infants in the developing world is sixteen times greater than it is for infants in the West, she told the delegates. And at least one woman dies every minute from avoidable complications of pregnancy. Half of these deaths occur in Africa, where hundreds of millions of children, and almost as many adults, suffer needlessly from illnesses that most people in the West have never heard of. The W.H.O.'s director general, Lee Jong-wook, warned that even the modest health goals that the United Nations has established for the new millennium are unlikely to be met. In fact, he said, in many places death rates are rising.

The most anticipated speech--and the least diplomatic--also came on the first day: Bill Gates addressed the assembly in his role as the founder of the world's most powerful charity, the Bill & Melinda Gates Foundation, which he and his wife started five years ago. The foundation's endowment is nearly twenty-nine billion dollars--more than the gross domestic product of Tanzania--and its principal goal is simple: to rid the world of disease, particularly the many illnesses that are essentially ignored because they affect the world's poorest people. "Global health is our lifelong commitment,'' Gates told me that day. "Until we reduce the burden on the poor so that there is no real gap between us and them, that will always be our priority. I am not so foolish as to say that will happen. But that's our goal.''

Gates had arrived from Seattle just after dawn, going directly to a breakfast with health ministers from ten African nations. It was a dismal day; rain pounded the gilt windows of the Palais des Nations, and the sky seemed heavy enough to touch the ground. The meeting was held in a room panelled in dark-green wood and filled with enormous mirrors. A buffet of coffee, tea, fruit, and doughnuts had been set out for the ministers. In front of Gates's seat, there was a Diet Coke and a plastic cup. When Gates entered, the ministers started to clap. Gates bowed his head, winced, and sat down. "I know your jobs are super, super important,'' he told them. "And I am excited about the progress that can be made for the health of your people.'' He looked tired, and seemed slight in a mauve shirt and gray business suit. One by one, the ministers told him their troubles. "In Nigeria, the health system simply doesn't work,'' Eyitayo Lambo, the country's health minister, said. His counterpart from Botswana, Sheila Tlou, echoed those thoughts. "H.I.V. and malaria have dismantled our country,'' she said. "We need help just to get back to where we were.'' The other ministers told similar stories. Tuberculosis, H.I.V., and malaria were rampant, as were lymphatic filariasis, schistosomiasis, river blindness, and other, even less well-known diseases. Each person began and ended by thanking Gates; in January, the foundation had contributed seven hundred and fifty million dollars to the U.N.'s Global Alliance for Vaccine and Immunization, to fight easily preventable diseases, like diphtheria, whooping cough, and measles. (Gates had also provided funds to vaccinate forty-two million children against hepatitis B.) The ministers thanked Gates for helping to promote a safe, cheap drug for visceral leishmaniasis (a malaria-like disease that affects nearly half a million people a year), for investing in the first seemingly effective new drug for sleeping sickness in fifty years, and for supporting research into a vaccine for pneumonia that could reduce African deaths by fifteen per cent.

Two days earlier, the Tribune of Geneva had run an article headlined "the health of the world depends more on bill gates than on the world health organization.'' Few of those at the assembly could disagree. The annual budget of the W.H.O. is $1.65 billion. Since 2000, the Gates foundation has spent six billion dollars to address health issues in the Third World--more than nearly every contributing nation, and far more than any other charity. This time, Gates arrived in Geneva with a check for two hundred and fifty million dollars, to help pay for the foundation's most ambitious venture yet: the Grand Challenges, a series of fourteen fundamental obstacles to scientific progress which, if solved, would lead to dramatic improvements in the health of the world. The challenges, which include goals like developing vaccines that require no needles or refrigeration, were first issued in 2003 (along with a two-hundred-million-dollar grant), and a thousand scientists from seventy-five countries responded with proposals.

It would be hard to overstate the impact that the Gates foundation has had: the research programs of entire countries have been restored, and fields that had languished for years, like tropical medicine, have once again burst to life. In a world where a fast reaction to the threat of disease is imperative, bureaucracies like the W.H.O.--which make decisions by consensus--are often too cumbersome to compete at the speed of a mutating virus. Gates and his wife need consensus only between themselves. At times, the foundation appears as brazen as Gates has always been at Microsoft, which he started thirty years ago, and where his combative style has made him one of the most polarizing figures in the history of American business. "Bill and Melinda don't believe in half measures,'' Richard Klausner, the former head of the National Cancer Institute, who is the foundation's director of global health, told me. "Every time we get a grant proposal, we ask what fraction of the problem will be solved by this work. Always. And if there is no answer there is no grant.'' The rock star and anti-poverty evangelist Bono put it another way: "This isn't about compassion. It's about results. It's not some sort of well-meaninghippie stuff. Bill Gates is not into nice sentimental efforts or whimsical support of hopeless causes. When Bill walks into the room, we are not expecting to have a nice warm fuzzy feeling."

Gates was scheduled to address the assembly at 3 p.m. First, however, there were some politics to endure. While he and I sat in a conference room on the second floor of the Palais, the delegates below were bogged down, for the eighth straight year, in hours of bickering over whether Taiwan could take part in the meeting. The country was not even seeking the right to vote--just to observe. Taiwan has always been a center of influenza--including the current epidemic of bird flu--and played a role in the rapid spread of SARS in 2003. It is not recognized by the United Nations, however, and there was never any chance that the request would be approved. Lofty goals are often set in Geneva--on H.I.V., polio (an effort now heavily underwritten by the Gates foundation), maternal health, and malaria, for example--but they are rarely met.

Malaria, the world's most prevalent parasitic disease, kills as many as three million people every year--almost all of whom are under five, desperately poor, and African. In most years, more than five hundred million cases of illness can be attributed to the disease, although exact numbers are difficult to assess because many people don't (or can't) seek care. It is not unusual for a family earning less than two hundred dollars a year to spend a quarter of its income on malaria treatment, and what they often get no longer works. In countries like Tanzania, Mozambique, and the Gambia, no family, village, hospital, or workplace can remain unaffected for long. Malaria governs their lives. "It just blows my mind how little money has been spent on malaria research,'' Gates told me as we were waiting for the Taiwan debate to end. "What has prevented the rich world from attempting this? I just keep asking myself, Do we really not care because it doesn't affect us? Is that what it is?'' Gates looked grim but went on. "Human suffering as a result of malaria is incomparable. By many measures, it's easily the worst thing on the planet.'' When Gates gets animated, his voice starts to slide in unexpected directions, and so does he. By the end of our conversation, he was talking in bursts and rocking back and forth in his chair. "I refuse to accept it,'' he told me. "I refuse to sit there and say, O.K., next problem, this one doesn't bother me. It does bother me. Very much. And the only way for that to change is to stop malaria. So that is what we are going to have to do."