Décadas antes de se tornar um renomado estudioso da lepra, o paranaense Heraclídes de Souza-Araujo vivenciou os dilemas próprios de qualquer indivíduo impelido a fazer escolhas profissionais: onde estudar, que carreira seguir, o que pesquisar. Mesmo depois de optar pela medicina, nosso personagem dedicou-se a temas sanitários que despertavam grande interesse entre os médicos e cientistas brasileiros nos primeiros anos do século XX, mas que não guardavam relação direta com a hanseníase, que se tornaria seu principal objeto de pesquisa ao longo da vida. Granuloma venéreo, malária, doença de Chagas, febre tifóide, sífilis e gripe espanhola foram algumas das doenças estudadas e combatidas por Souza-Araujo nos primeiros anos de sua carreira. Este trabalho se dedica, essencialmente, ao período compreendido entre 1910 e 1921. O primeiro marco teve como referência o ingresso do personagem na Faculdade de Medicina do Rio de Janeiro. O segundo, a saída de Souza-Araujo do cargo de chefe do Serviço de Profilaxia Rural em seu estado natal. No decorrer destes anos, em instituições localizadas no Rio de Janeiro, Paraná, Alemanha, Argentina e Uruguai, foram forjadas as bases da identidade sanitarista-leprologista, sustentada pelo personagem até o final de seus dias.Decades before becoming a renowned scholar of leprosy, Heraclides de Souza-Araujo experienced the dilemmas inherent in any individual compelled to make career choices: where to study, what career to follow and what to research. Even after choosing medicine, our character devoted his studies to health issues which aroused great interest among clinicians and scientists in Brazil in the early years of the twentieth century, but not directly related to leprosy, which became his main subject of research throughout life. Granuloma venereum, malaria, Chagas disease, typhoid, syphilis, and Spanish flu were some of the diseases studied and addressed by Souza-Araujo early in his career. This work is mainly dedicated to the period between 1910 and 1921. The first milestone refers to the character's entry in the Faculty of Medicine of Rio de Janeiro. The second is Souza-Araujo’s leave as the chief of the Rural Prophylaxis Service in his home state. During these years, in institutions located in Rio de Janeiro, Parana, Germany, Argentina and Uruguay, the basis of his identity as a leprologist sanitarist was fabricated. Such identity was supported by the character until the end of his days. What are the institutional and cognitive paths taken by Dr. Heraclides? Which characters participated and helped in building his career? How was his professional identity shaped? These are some questions whose answers may be found in the following pages.