To assess the response to and tolerance of recombinant interferon-alpha administration in patients with chronic hepatitis C and human immunodeficiency virus (HIV) infection, 12 patients with chronic hepatitis C and HIV infection were given interferon-alpha, 1, 3, or 5 million units thrice weekly, for 4 or 6 months. Four patients had a complete response (normal serum alanine aminotransferase activity [ALT]), 3 had a near-complete response (serum ALT less than one-and-one-half times the upper limit of normal), and 5 had no response at the end of administration. Histologic examination of liver showed an improvement in 1 patient with complete response and no improvement in another patient with no response. In patients with chronic hepatitis C with HIV infection, the response to and tolerance of recombinant interferon-alpha were not different from those usually observed in patients with chronic hepatitis C infection without HIV infection.