The present work analysed endomyocardial biopsies of patients with acute Chagas' disease in order to evaluate the frequency and intensity of T. cruzi antigens, CD4+ and CD8+ T cells to determine the characteristics of this recurrent disease in Venezuela. Twelve endomyocardial biopsies of patients with Chagas' disease, 12 to 51 years old, (7M and 5F) were analysed. T. cruzi antigens and CD4+ (helper) and CD8+ (cytotoxic-suppressor) T cells were detected by the immunoperoxidase technique. The presence and intensity of lymphocytic myocarditis was evaluated according to the degree of myocardial fibre injury caused by inflammatory infiltrate. Myocarditis was present in 100% of the cases. The mean numbers of CD4+ T cell and CD8+ T cell were 11.00 (+/- 10.29); 14.69 (+/- 13.08) and the CD4/CD8 T cell ratio was 0.75. T. cruzi antigens were detected in 58%. There was a good correlation between the numbers of CD4 and CD8 T cells of each case and a lack of correlation with the amount of T. cruzi antigens. All patients with acute Chagas' disease show some degree of myocarditis that seems to be directly related to the presence of parasitic antigens. Both CD4 and CD8 T cells participate in this process. We are following these patients to see if patients with severe myocarditis and more parasite antigens in the acute phase will develop chronic heart failure.