A striking association between hepatitis C virus (HCV) and mixed cryoglobulinemia (MC) has been reported by various authors, regardless of the presence of chronic hepatitis. The aim of this study is to evaluate the prevalence of HCV-related markers in cryoglobulinemic membranoproliferative glomerulonephritis (MPGN) which is one of the most severe complications of MC. Antibodies against HCV have been detected by second-generation Chiron ELISA and RIBA in 26/26 (100%) cryoglobulinemic MPGN. In addition, serum HCV RNA, expression of the ongoing viral replication, was present in 7/7 patients by the polymerase chain reaction technique. The high percentage of anti-HCV seropositivity suggests that this virus may play an important role in the pathogenesis of this immunemediated glomerulonephritis.