Whereas C-reactive protein (CRP) is acknowledged as a cardiovascular risk marker, there is ongoing discussion about its role as a risk factor. Previous studies focused on the effects of CRP on ischaemic heart failure and atherosclerosis. In this study we investigated distribution of CRP, the Terminal Complement Complex (C5b-9) and macrophages (CD68) in the myocardium of patients suffering from non-ischaemic heart failure and their implication on clinical parameters. Endomyocardial biopsies were taken from 66 patients suffering from dilated cardiomyopathy (DCM). Biopsies were analysed by immunohistochemical and immunofluorescent staining for CRP, C5b-9 and CD68. Viral DNA/RNA for adenovirus, enterovirus, parvovirus B19 and human herpes virus 6 was detected by PCR and Southern blot analysis. Myocardial biopsy findings were correlated with plasma level of hsCRP and NT-proBNP as well as echocardiography, exercise test and NYHA class. In 18 (27%) patients, a positive staining for CRP and in 57 (86%) patients a positive staining for C5b-9 was detected. All patients showed myocardial infiltration with macrophages with an average of 39 cells/mm(2). CRP, C5b-9 and CD68 co-localised within the myocardium. No correlation was observed for inflammatory proteins and plasma level of hsCRP, NT-proBNP and clinical parameters. CRP is frequently present in the myocardium of patients suffering from DCM and co-localises with C5b-9 and macrophages. CRP may contribute to myocardial damage in DCM via activation of the complement system and chemotaxis of macrophages.