Emilio Marcondes Ribas was born in Pindamonhangaba, São Paulo, on April 11, 1862. After graduating medical school in Rio de Janeiro in 1887, he began practicing medicine in the interior of São Paulo. He became a sanitary inspector in 1895 and three years later was named head of the São Paulo State Sanitary Service, a post he held for nearly twenty years. During this time, he modernized the state’s public health structure and successfully fought a number of epidemics. One of his initiatives was to found the Butantan Institute in 1899, initially intended to be a laboratory for the production of plague serum. Ribas was one of the earliest Brazilian defenders of the mosquito theory of yellow fever transmission. In 1903, he conducted an odd experiment to prove the thesis: he and Adolpho Lutz allowed themselves to be bitten by infected mosquitoes. In addition to yellow fever and other illnesses, he also studied tuberculosis and Hansen’s disease. He died in São Paulo on December 19, 1925.