This essay complicates our thinking about unequal North-South ‘collaborations’ by considering how distinct scientific traditions, national politics, forms of racial thinking, and conditions of internal colonialism in the global South shape relations with individuals and entities based in the global North. It does this by examining conflicts between Peruvian scientists and the United Nations’ Commission for the Study of the Coca Leaf, which visited Peru and Bolivia in 1949 to investigate the health effects of coca consumption on highland Indigenous populations. Sent at the Peruvian government’s invitation, commission members saw themselves as conducting a field survey. However, they quickly found themselves embroiled in conflict with a Peruvian high-altitude physiologist, Carlos Monge, who sought long-term, laboratory-based collaboration. Monge’s scholarship and experiments proved controversial for UN authorities because they emphasized the racial alterity of highland Indigenous peoples even as he and his peers disagreed about the health effects of coca chewing.