Two Japanese patients suffered from membranous glomerulonephritis associated with hepatitis C virus (HCV) infection. Renal histologic changes were characterized by granular deposits of IgG and C3 along the capillary wall and numerous subepithelial deposits in glomeruli. Hypocomplementemia was present in one patient, but both cryoglobulins and rheumatoid factors were absent. HCV RNA was detected in both their sera by RT-PCR, both free and in the form of circulating immune complexes. The HCV core protein was found in the glomeruli from both patients by indirect immunofluorescence. These results suggest that in some patients chronic HCV infection causes membranous glomerulonephritis through immune complex deposition involving HCV proteins.