This social science paper aims to highlight the exceptional encounter between a research team on hiv/aids and an humanitarian ngo. As the matter of fact an Unit of French Research Institute for Development (ird, France) and the Helvetic section of Médecins Sans Frontières had put together their scientific knowledge and their humanitarian commitment in 2001 in Yaounde (Cameroon). Their common objective was to propose an original response and example facing one of the worst health tragedy of these last decades : Treat hiv/aids patients in Africa with Antiretroviral Treatment.