Summary This article looks at a specific case of intellectual exchange by approaching Luís Pereira Barreto (1840?1923), a Brazilian medic who, having studied in Brussels in the 1850s, came into contact with Comte's positivism and with the ideas of his disciples. While in Europe, Barreto established a long-lasting friendship with Pierre Lafitte, and became a convert to Comte's Religion of Humanity. Upon his return to Brazil in 1864, Barreto sought to apply Comte's principles to Brazilian society and politics. Although Barreto's (...) use of positivism extends beyond the issue of slavery and slave work, I will focus on this priest of humanity's considerations about positivism, social evolutionism, and Brazilian slavery. This will allow me to extrapolate some qualified conclusions about the nature of the intellectual exchange that occurred between Barreto and the French positivists, and the development of Brazilian positivism as a political philosophy and social theory which had to address the problem of slavery in the 1870s and 1880s. (shrink)