The main objective of my research project is to examine the intersection of medical parasitology, ideology, and politics in Brazil during the twentieth century from the perspective of two of its most important representatives: Samuel Barnsley Pessoa (1898-1976) and Amilcar Vianna Martins (1907-1990). Both are considered founding fathers of modern medical parasitology in Brazil. Pessoa taught at the School of Medicine of the University of São Paulo, Martins at the School of Medicine of the Federal University of Minas Gerais in Belo Horizonte. Both were the chairs of medical parasitology in their respective medical schools. From the 1940s onwards, both, too, were active militants of the clandestine Brazilian Communist Party (PCB). In the mid-twentieth century, a considerable number of leading Brazilian parasitologists, most of whom were trained by Pessoa and Martins, were also associated with the Communist Party in the 1950s and 1960s. At the center of this story lies a major paradox: just as these parasitologists were recognized nationally and internationally for their research and contributions, they were also persecuted, both internally and externally, for their communism. Most of them were harassed, imprisoned, dismissed, or exiled by the military regime that was established in March 1964, ending the era of democracy inaugurated in 1945.