The etiology of idiopathic dilated cardiomyopathy (DCM) is yet unknown; this study aimed at further differentiation of the disease by means of enzyme histochemistry. Endomyocardial biopsies from the left ventricle of 40 DCM patients and 5 control specimens had enzymes examined histochemically and semiquantitatively and analyzed according to staining intensities of nicotinamide adenine dinucleotide tetrazolium reductase (NADH-TR), succinate dehydrogenase, cytochrome c oxidase, lactate dehydrogenase and acid phosphatase (aPh). In DCM, the NADH-TR activity was elevated as compared to controls, indicating impaired mitochondrial oxidative phosphorylation. However, a concrete relation of enzyme histochemical intensity to anamnestic, hemodynamic or histomorphometric data could not be determined, except for the fact that the intensity of the lysosomal enzyme aPh was elevated in DCM patients with a relatively high left ventricular ejection fraction. The results demonstrate an interindependence of structural, hemodynamic and historical parameters as well as enzyme concentrations in DCM. Thus, a pathological change in the enzyme concentrations tested here cannot be responsible for the functional myocardial impairment in DCM.