In the municipalites of Duque de Caxias and Nova Iguaçú, which are a part of the Greater Rio de Janeiro, dwellings were found infested by T. infestans. T. infestans infected by flagellates morphologically indistinguishable from Trypanosoma (S) cruzi were found in two localities in the municipality of Duque de Caxias (Amapá and Piranema). It was noted that some of these insects were collected in a house in which the dwellers have never been in a zone affected by Chagas' disease. The authors conclude that the infestation is probably recent and discuss the problem of this Triatoma prolifering in a climate opposite to its area of disrpersion and in a region where sylvan triatoma, which penetrates into the dwellings, is not able to form colonies.