Thirty patients affected by hemophilia A or B or von-Willebrand's disease and chronic posttransfusional active HCV hepatitis who developed major side effects during the course of a previous treatment with recombinant interferon-alpha (IFN-alpha) were studied. In all patients IFN-alpha therapy had to be discontinued and those who achieved a primary serologic and viral response to HCV relapsed within a few months. After a washout period, patients were retreated with human leukocyte IFN-alpha, 6 MU thrice weekly for 12 months. In about 90% of patients, a primary response, with normal AST and GGT values and undetectable HCV-RNA, was achieved within the third month of treatment and for the entire duration of treatment none of the patients had to discontinue therapy because of severe adverse reactions. During posttherapy follow-up only one patient relapsed. The human leukocyte IFN-alpha regimen looks to be very effective and safe for carriers of inherited clotting disorders who developed major side effects with recombinant IFN-alpha therapy for HCV-related chronic hepatitis.