Results of a survey on the occurence of Chagas' disease in patients of the hospital "Santa Casa de Misericórdia" in Belo Horizonte, Minas Geraes, Brazil, are reported. 181 unselected patients have been examined. The following methods have been used: a) general clinical examination and special examination of the circulatory apparatus; b) electrocardiogram; c) complement-fixation test for Chagas's disease (Schizotrypanum cruzi culture antigen); d) Wassermann test; e) xenodiagnosis and X-ray pictures of patients with positive complement-fixation test for Chagas's disease or with heart troubles of any kind. 37 out of the 181 (20.44%) patients examined had positive laboratory tests for Chagas' disease. 49 (27,07%) had heart troubles with the following etiology: Chagas' disease (18 cases); arteriosclerosis (13 cases); hypertension (12 cases); syphilis (6 cases); rheumatic fever (3 cases); congenital heart disease (1 case); chronic cor pulmonale (1 case). .18 pit of 34 Chagas' disease patients (52,95%) showed evidences of myocardial damage. The most frequent electrocardiographic changes were right bundle branch block, ventricular premature beats, alterations of QRS (single or associated to alterations of T wave), auriculo-ventricular blocks. These findings are similar to those previously described in chronic Chagas' heart disease by Laranja et al. (13,26). The most frequent electrocardiographic changes found in the group of patients with negative tests for Chagas' disease were those showing left ventricular strain, primary alterations of T wave and ventricular premature beats. 50.0 per cent of the patients with chronic Chagas' heart disease were under 30 years of age and 80,33 per of the patients with heart lesion from other causes than Chagas' disease were over 30 years. The complement-fixation test (SChizotrypanum cruzi culture antigen) owing to its specificity and sensibility proved to be very useful for the laboratory diagnosis of chronic Chagas' disease. Xenodiagnosis was positive in 8 out of 31 (25.8%) patients with positive complement-fixation tests. The question of the etiology of megaoesophagus and megacolon has been discussed and the writers admit that schizotrypanosis may possibly be of significance in the development of these conditions. The geographic distribution of Triatomid-bugs in Minas Gerais has been briefly recorded. the principal vectors are Panstrongylus megistus, Triatoma infestans and Triatoma sordida although 12 other species occur in this State. These insects exist in 204 of the municipalities (64,55%). Infected vectors have been found in 143 municipalities (70.09%). The most important infected areas have been named and chartered. The writers emphasize the medical and social importance of Chagas' disease and express the belief that it is one of the most important factors of heart disease in the rural zones of the State of Minas Geraes.