A cross-sectional study was carried out on the residents of one in every four dwellings in the town of Barcelos (in the northern part of the State of Amazonas, on the right bank of the Rio Negro, 490 kilometers from Manaus by river), in order to evaluate social and sanitary conditions and specific indicators for intestinal parasites and Chagas' infection. During the survey, two questionnaires were applied, a household one to evaluate social and sanitary aspects, and an individual one, for social and epidemiological evaluation of the population conditions. A conglomerate family sample of 171 dwellings was studied. From each of the 658 habitants, a sample was requested for stool examination by Lutz sedimentation and Baermann-Moraes-Coutinho techniques modified by Willcox & Coura (1989), and blood was collected in filter paper for immunofluorescence test by Camargo (1966) and Souza & Camargo (1966) methods modified by Petana & Willcox (1975). The stool examination showed 69.4% of samples with one or more parasites. Ascaris lumbricoides was predominant with 51% of positivity and Entamoeba histolytica, although surveyed by a non-specific method, was present in 19.7%. Surprisingly, 20.1% of the 658 sera samples were reactive for T. cruzi antibodies at a dilution of 1:20 and 13.7% at 1:40. There was a strong correlation between this result and the level of human contact with wild triatomines, known locally as "piasava lice", and we succeeded in isolating by xenodiagnosis one strain of T. cruzi from one patient, a sixty-one-year old man (n. 209 -1), a native of the area, with positive serology for Chagas' disease and who worked in agriculture and transporting piasava and was very familiar with "piasava lice".