After discussing, in a general way, the problem of the notorious nomadic habits of the Brazilian population, illustrating with some statistical data the proportion of the chief migratory streams observed inside Brazil, the Author analyses the influence of such migrations in the epidemiology of parasitic diseases. For this purpose he considers the migratory movements involved in the following types of human activities: 1) pushing forward the agricultural frontier either by the expansion of sections already settled or by the establishment of new colonial nuclei in remote points of pioneer areas; 2) itinerant or "fire" agriculture caracterized by a constant opening of new clearings in forests and the abandoning of old areas already exhausted by farming; 3) gathering of plant products and prospection of mineral resources; 4) construction of pioneer railroads and high ways, with the establishment of new settlements along their sides; 5) construction of Brazilia and colonization of Central and Western Brazil; 6) rationalization of agriculture and industrialization of urban areas inducing rural-urban migration.