BACKGROUND: Autoreactive humoral and cellular immune responses may be involved in the pathogenesis of idiopathic dilated cardiomyopathy (IDC). Certain human leucocyte antigens (HLA) could also be linked to the development of IDC. AIM: To determine whether various markers of autoimmunity are present in the final phase of the disease, to substantiate the role of an autoimmune process in IDC. METHODS: 37 patients with end stage IDC were studied, together with 39 patients with end stage heart disease of known aetiology who were included for comparison. Multiple myocardial tissue samples from the explanted heart of each patient were evaluated (immuno)histologically. An indirect immunofluorescence assay was used to screen patient serum samples for the presence of heart specific autoantibodies. HLA class I and II frequencies were determined in each group and compared with HLA frequencies from healthy blood donors. RESULTS: Only scanty small mononuclear cell infiltrates were present in myocardial tissue of seven patients with IDC and of 11 patients with heart disease of known cause. The majority of these inflammatory cells were negative for T cell markers. All blood specimens were negative for heart specific autoantibodies and there was no apparent association of IDC with particular HLA phenotypes. CONCLUSIONS: These findings suggest that an active autoimmune process is not involved in the end stage of IDC.