Trypanosoma cruzi causes a profound immune depression in the infected host, and a small proportion of chagasic patients will develop a chronic disease characterized by myocardiopathy. There is evidence suggesting that dilated non-chagasic cardiomyopathy may be mediated by an immunological mechanism. In an attempt to distinguish abnormal immunoregulatory cell patterns in both dilated myocardiopathies, total and activated T and B lymphocyte subpopulations were measured by flow cytometry and double-labeling in whole blood samples from patients with dilated myocardiopathy, 10 with positive serological tests for T. cruzi and 9 with different non-chagasic cardiomyopathies. Several significant differences were found between both groups of patients and 13 sex-and age-matched apparently healthy controls. Chagasic patients besides showing clear decrease in absolute numbers of CD31/CD711 and CD81/CD251 cell populations also had a significant increase in CD191, CD101, and CD191/HLA-DR1 cell subsets, as well as high helper/ suppressor cell ratio. These findings suggest that concurrently with T cell diminution, which involved activated T lymphocytes displaying suppressor/cyotoxic immnunophenotype, chronic chagasic patients with myocardiopathy showed elevated numbers of total and activated B lymphocytes. Patients with dilated non-chagasic myocardiopathy had significantly increased numbers of activated T cells (CD31/CD251, CD81/CD251, and CD81/HLA-DR1) and total and activated B lymphocytes (CD101, CD191, CD191/HLA-DR1). These data support the notion that dilated myocardiopathies other than the chagasics may be associated with immunological abnormalities.