Serum immunoglobulins G, A, M and E were determined in four groups of children, including 14 patients with dilated cardiomyopathy (DCM), 17 with endomyocardial fibrosis (EMF), 18 with rheumatic heart disease (RHD) and 35 age-matched controls, in an attempt to assess the role of infections in the aetiology of childhood cardiomyopathies. Mean IgA and IgM concentrations in all four groups were not significantly different. However, mean IgG concentrations were higher in patients with EMF (1729 mg/100 ml), DCM (1745 mg/100 ml) and RHD (1978 mg/100 ml) than in controls (1429 mg/100 ml), and in about 30% of these cardiac patients the levels were higher than the 97th percentile for controls. In addition, mean serum IgE was higher in EMF (3577 iu/ml) than in RHD (2814 iu/ml), DCH (1000 iu/ml) or controls (1666 iu/ml), and in 29% of the EMF patients serum IgE exceeded 6834 iu/ml, the 89th percentile for controls. Intestinal helminths and moderate eosinophilia (mean count, 10%) were detected in most of the EMF patients. These results suggest that some cases of EMF and DCM are, like RHD, complications of infections, and that intense helminth-induced anaphylaxis is a probable cause of cardiac damage in such cases of EMF.