The results of the Serological survey for the prevalence of chagasic infection in Brazil, 1975/1980, were published before (Camargo et al, 1984) but the detailed geographical distribution is described in this paper. This was an initiative of two governmental bodies: the Superintendencia de Campanhas de Saúde Pública a Ministry of Health Division in charge of all public health policies, and, the Research National Council of the Ministry of Science and Technology through a program called Integrated Program for Endemic Diseases. Results obtained were extremely useful for a precise delimitation of the area with endemic transmission of Chagas disease, and hence, to direct the activities for vector control, which were implemented from 1975 onwards. This survey showed an estimated seroprevalence of 4.2% of T. cruzi infection in the rural population in the country. Only two federal units were not included, São Paulo and the Federal District (Brasilia) for which enough recent information was available. This survey included all the other federal units of Brazil, with the examination of 1,626,745 blood samples by indirect immunofluorescence. From them, 1,352,197 were validated for processing and statistical analysis, which were from 3,026 municipalities of 24 states, as by the political division of the country by this time. Overall results obtained, confirmed data that were well known, but some were non expected. These last were subject of further investigations, until confirmation, based also on entomological data and a better interpretation of the results obtained.