The autors described a potencial focus of american trypanosomiasis in Santa Tereza, populous residencial zone, situated near of the center of Rio de Janeiro city. Fifteen specimens of opossum (Didelphis marsupialis L;) were found naturally infected with Trypanosoma (Schizotrypanum) cruzi (Chagas 1909). A variety of opossum (Metachirus nudicaudatus Geoffroy), was referred to also, by the first time, as wild host of these trypanosomes. Eleven specimens of triatoma (Panstrongylus megistus (Burmeister 1835), from whom nine infected, were captured in a large building situated in the same local. Careful inquiry realized in the local, on permitted to affirm that the breeding-places of these triatomoe, were localized in the forest. In these there, exists poor habitations, in which the occurrence of accidental clinical cases of Chagas´ disease is possible.