One hundred patients with the indeterminate form of human chronic Chagas disease were submitted to chemotherapy, 50 with nifurtimox (Bayer) and 50 with benznidazole (Roche) from 1965 up to 1985. After two-year follow-up there was negativation of xenodiagnosis in 25 (50%) and negativation of serological tests in 3 (6%) of the patients treated with nifurtimox. As for benznidazole there was 35 (70%) of xenodiagnosis negativation and 5 (10%) of serological negativation. In 92 patients after a period of 24 month follow-up there was at least one kind of positive test, indicating therapeutic failure. Eight patients with negative xenodiagnosis and serological tests were considered cured. The average follow-up in patients treated with nifurtimox and benznidazole were respectively 17.3 and 7 years.