(FORTUNE Magazine) – CANCER For Jim Stowers the key to successful philanthropy has been to treat it as he does his family of mutual funds, American Century investments. He gives donors "Hope Shares" and annual statements that let them see their contribution grow as part of the endowment of Stowers Institute for Medical Research. Helped by a whopping $1.6 billion that he and his wife, Virginia--both cancer survivors--have committed since 1994, the Kansas City, Mo., institute, which began with cancer research, today conducts work on a wide range of diseases.

AIDS Despite ever-rising worldwide AIDS rates, the disease's visibility has plunged in the U.S., owing in part to the erroneous notion that any leveling-off in U.S. infections signals a stemming of the global epidemic. But mega-givers haven't been fooled. The Bill & Melinda Gates Foundation has provided $980 million to fund the global fight and has focused aggressively on finding a vaccine against AIDS. George Soros's Open Society Institute and his other foundations have devoted $21 million primarily to aiding at-risk and infected populations.

DIABETES With the incidence of type 1 (or juvenile) diabetes on the rise and occurring in younger and younger children, the need for a cure has become even more pressing. Former Chrysler chief Lee Iacocca, who lost his wife to complications from diabetes, founded the Iacocca Foundation in 1984 and has given $20 million to the cause. Last year a researcher supported by the foundation succeeded in reversing type 1 diabetes in mice. This year Iacocca launched "Join Lee Now," a campaign to raise $11 million for clinical trials through small donations from ordinary Americans.

MALARIA Because malaria and other Third World infectious diseases primarily affect only the poorest nations, they haven't traditionally attracted the large gifts common to ailments of the upper classes. The Bill & Melinda Gates Foundation launched a major effort to reverse that in 2003 with a $168 million donation to combat malaria, more than doubling the total amount spent on malaria research each year and leading to the recent creation of a potential vaccine. With a $250 million contribution, Gates also launched "Grand Challenges in Global Health"--a program that invites scientists to pitch research projects addressing the problems of the world's poorest areas. All told, the foundation has committed $4.1 billion to fight disease in the developing world.

STEM CELL RESEARCH One of the most promising and controversial fields to emerge in recent years, stem cell research has drawn a spate of big donations from corporate philanthropists, who laud its potential to advance treatment of a wide variety of ailments, from Alzheimer's to heart disease. Intel chairman Andy Grove took his gift to the public, pledging $5 million in matching funds to launch a stem cell biology research program at the University of California at San Francisco in 2002. Under the "Grove Stem Cell Challenge" banner, the effort exceeded its $10 million goal in 18 months. (For the latest on stem cell advances, see "Stem Cells to Fix the Heart.")

NEUROLOGICAL DISORDERS Growing interest in studies of the brain and its chemistry stems from a desire to better tap the organ's immense, complex capacities, as well as from a wish to understand and aid the developmentally disabled. Microsoft co-founder Paul Allen gave $100 million in 2003 to create the Allen Institute for Brain Science in Seattle. Its first goal: to create a revolutionary 3-D map of the mammalian brain called the Allen Brain Atlas. The project recently won a $1.8 million grant from the U.S. Army, which hopes to use the map in studies of sleep deprivation.