Immunological factors have been involved in the pathogenesis of dilated cardiomyopathy (DCM). The cytotoxic action of macrophages is one of the main factors causing cardiac myocyte damage. Monocyte chemoattractant protein-1 (MCP-1) is a major signal for the accumulation of monocytes/macrophages. We examined whether MCP-1 was expressed in the myocardium of DCM patients and whether the expression level was correlated with the degree of impairment of cardiac function. The expression of MCP-1 in the myocardium was determined by immunohistochemistry in endomyocardial biopsy samples from 13 patients. The expression of MCP-1 was found in all myocardial samples from DCM patients but not in those from control subjects. Positive staining for MCP-1 was distinct in cardiac myocytes, interstitium and infiltrating cells. Semi-quantitative analysis revealed that the expression of MCP-1 was inversely correlated with left ventricular ejection fraction. In conclusion, the expression level of MCP-1 in the myocardium was correlated with the degree of impairment of cardiac function in patients with DCM.