[Oswaldo Cruz and the serology controversy].

This analysis of the discussion surrounding the efficacy of the plague serum produced by Manguinhos Institute in the early twentieth century begins with an overview of Oswaldo Cruz's service as head of the Public Health Directorship (Diretoria de Saúde Pública). The controversy itself is then addressed, through an exploration of correspondence exchanged by physicians Oswaldo Cruz, Miguel Pereira, Vital Brazil, Chapot Prévost, and Francisco Fajardo. Their letters reveal how bacteriology in Brazil was then marked by uncertainty and experimentation, even while this field of knowledge publicly touted itself as safe and incontestable. The article shows how arguments of an extra-scientific nature interfere with both research development and the acceptance of medical products.