Background : Inflammatory reactions and viruses have known to play significant roles in pathogenesis of non-ischemic dilated cardiomyopathy (DCM). We analysed myocardiums for inflammations by immunohistochemical staining (IHCS) and viruses by polymerase chain reaction (PCR) in patients with non-ischemic DCM. Methods : Myocardial biopsies of 21 patients were analyzed for CD3, CD45, HLA-DR, ICAM-1, VCAM-1, CD62-E, LFA-3 with IHCS method and for enterovirus, adenovirus (ADV), parvovirus B19 (PVB19), cytomegalovirus, Epstein-Barr virus, herpes simplex virus (HSV), human herpesvirus 6 with PCR method. Results : Mean age of patients were 45 (range: 17-67). Patients with duration of symptoms less than 6 months were 14. Myocardial biopsies of 2 patients were consistent to myocarditis by Dallas criteria in HE staining. Of 19 biopsies without myocarditis, CD3, CD45, HLA-DR, ICAM-1, VCAM-1, CD62-E and LFA-3 were positive in 1, 6, 2, 1, 1, 3 and 2 biopsies, respectively. ADV was detected in 1 patient with myocarditis. PVB19 and HSV type 2 were detected in 5 and 1 of 19 patients without myocarditis. Patients were attributed to four groups according to the results of IHCS and PCR. Patients with inflammation and no virus, patients with inflammation and viral genome, patients with virus and no inflammation and patients without inflammation and virus were 6, 4, 2 and 7, respectively. Conclusion : The applications of IHCS and PCR methods to myocardial biopsy were feasible and permits the more accurate pathologic diagnosis in patients with DCM.