The Royal Society of London held a scientific meeting in September 2000 focusing on two theories of the origin of AIDS: one, that it occurred through "natural transfer" of immunodeficiency virus from monkeys or chimpanzees to humans; and the other, that it occurred through iatrogenic transfer via contaminated polio vaccines used in Africa in the late 1950s. This meeting was the culmination of years of public contention over the polio-vaccine theory. Several dimensions of the politics of science are revealed by analysis of this issue, including the power of scientific editors, the use of the mass media, decisions regarding selection of speakers and organization of the meeting, and epistemological assumptions made by participants.