A 55-year-old female presenting with nephrotic syndrome one month after alpha interferon therapy for chronic hepatitis type C is reported. Leg edema and abdominal fullness appeared 1 month after alpha interferon therapy. Urinalysis revealed 4.8 g/day of proteinuria. Laboratory examinations disclosed hypoalbuminemia (1.9 g/dl), positive for HCV antibody and HCV-RNA. Cryoglobulins could not be found. Light microscopic findings of renal biopsy revealed mild expansion of the mesangial area and spike-like structure along the outer aspect of capillary walls. Immunofluorescent examination of the renal biopsy demonstrated granular staining of IgG along the capillary walls. She was diagnosed as having nephrotic syndrome due to membranous nephropathy. She was treated with oral administration of predonisolone in an initial dosage of 30 mg/day and cyclophos- phamide in an initial dosage of 50 mg/day. The therapy was markedly effective for this case. We discuss the relationship among HCV, interferon, and nephrotic syndrome. identifier:奈良医学雑誌 Vol.47 No.6 p.325-330 identifier:04695550 identifier:13450069 identifier:http://ginmu.naramed-u.ac.jp/dspace/handle/10564/759 identifier:奈良医学雑誌, 47(6): 325-330