Two bone marrow transplant recipients are described who developed nephrotic syndrome in association with hepatitis C virus (HCV) infection. Renal biopsies of both patients revealed stage I membranous glomerulonephritis. Detection of HCV genome was performed by nonisotopic in situ hybridization and reverse transcriptase polymerase chain reaction on paraffin-embedded renal biopsy specimens. Hepatitis C virus genome was detected by reverse transcription nested polymerase chain reaction on the RNA extracted from 15 5-microns paraffin sections. However, HCV genome was not revealed by nonisotopic in situ hybridization, which was likely due to the low copy number of HCV genomes present. These studies suggest that chronic HCV infection is associated with membranous glomerulonephritis.