Creation of the Rio de Janeiro Medical and Surgical Society serves as the basis for this study of late-19th-century medicine in Brazil. The hypothesis is that beginning in the 1880s changes to institutions and the diversification of medical community inaugurateed the structuring of a field of social relations specific to medical practitioners. With official medical institutions undergoing crises, alternative groups that emerged outside the government framework worked together toward common ends, particularly the construction of a kind of Brazilian medical knowledge that could play a role on the international scientific scenario.