Endomyocardial biopsies were performed in 11 African women in Nairobi who presented with the clinical features of peripartum cardiomyopathy. The samples were studied by light and electron microscopy. In five patients there was evidence of a "healing myocarditis", that is the presence of a mild inflammatory cell infiltration within the myocardium with foci of necrosis and variable amounts of hypertrophy and fibrosis. Of the nine patients who were followed up, three out of four with myocarditis had persistent heart failure and four out of five without myocarditis improved. Peripheral blood T lymphocyte cell subsets were measured in nine patients by means of monoclonal antibodies. A high helper:suppressor T cell ratio was found in three patients. Almost half of this group of patients with peripartum cardiomyopathy had myocarditis in their biopsy specimens. The myocarditis may have been due to an inappropriate immunological reaction in some patients.