International science policy controversies involve disputes over cultural differences in the assessment of knowledge claims and competing visions of the policy-making process between different nations. This essay analyzes these dynamics in the recent controversy surrounding AIDS policy in South Africa. It develops the notion of an epistemological filibuster, an appeal to uncertainty in order to delay policy implementation, and shows the key role it played in producing an argumentative stalemate between President Thabo Mbeki and Western orthodox AIDS scientists that threatened millions of HIV-positive South Africans. (Contains 87 notes.)