The authors after reviewing the finding on rodents of the family Cricetidae and geners Oryzomys infected by T. cruzi, report the infection of a specimen of the rat, Oryzomys nigripes (Desmarest, 1819), captured at Salto de Pirapora, State of São Paulo, Brazil, whose T. cruzi strain was isolated through xenodiagnosis. The trypanosome is pathogenic for baby wistar rats and white mice, infecting one hundred percent of the animals inoculated. Blood flagellates observed in mice have a mean total lenght of 24,25μ and a mean nuclear index of 1,27μ. Leishmanial forms were seen in cardiac fibres of mice killed during the acute fase of infection. The infection in mice was mild, with relatively long prepatent period (mean of 7,1 days), with low parasitemia, long duration of the acute phase and small letality index. Protection tests show that mice recovered from a infection voith the rodent strain develop a high resistance against reinfection by the Y strain. The trypanosome is easily cultivated in blood agar medium and in Warren's liquid medium. It infected regularly some species of triatomine tested, giving the following infection rates: P. megistus- 100,0 percent; T. infestans - 76,7 per cent; T. sordida - 86,7 per cent; R. neglectus - 100,0 per cent.