The pattern of ECG changes of 150 black individuals from rural areas of southern Rio Grande do Sul, Brazil, was compared with that of a group of 150 whites of similar age, sex and geographical residence. The mean age of the study group was 39.2 years (9-78 years), and 62% were women. 84 out of the 150 showed positive serological reactions to infection by Trypanosoma cruzi. The prevalence of ECG changes was significantly higher among the blacks, irrespective of their serological state. Those changes which were considered as suggestive of Chagas cardiopathy were more common among blacks with positive serological reactions. Blacks with seronegative reactions had more frequent ECG changes which were of increased severity, than those of whites with negative reactions. The increased prevalence and severity of ECG changes among black might be attributed to several factors, including: higher levels of poverty, leading to strenuous working conditions; poorer housing quality facilitating infestations by triatominae; inadequate feeding habits. In addition, the increased levels of arterial tension found among the blacks, might be associated with possible racial factors, in collaborating to increase the likelihood of myocardial lesions.