We investigated distribution of HLA class II alleles among 52 unrelated patients with dilated cardiomyopathy (DCM) (25 consecutive men, 27 consecutive women, mean age 38 +/- 16 years) to determine if there is any immunogenetic predisposition to the disease. DCM was diagnosed according to WHO criteria. HLA-DR and DQ alleles were examined by PCR-SSP typing. Frequency of DRB1* and DQB1* alleles in the study group was compared to local control group (n = 126 for DRB1* and n = 76 for DQB1* alleles). There was a non-significant increase in the frequency of HLA-DRB1*03 (chi square = 4.78, p < 0.05, p corrected for multiple comparisons (pcorr)--NS) and HLA-DQB1*02 (chi square = 4.92, p < 0.05, pcorr--NS) among DCM patients as compared to controls. Frequency of DRB1*04 allele was lower than expected (chi square = 4.58, p < 0.05, pcorr--NS). DRB1*03 is associated with several autoimmune diseases, of interest it confers risk for idiopathic myopathy in Polish patients. Heterozygosity for DRB1*03/DRB1*04, known for association with insulin-dependent diabetes mellitus was found in 3 patients (5.7%), two of them had adult-onset insulin-dependent diabetes mellitus. There was a tendency to overrepresentation of DRB1*08 among men with DCM. In conclusion, these data give some support for autoimmune involvement in the pathogenesis of dilated cardiomyopathy.