We studied a series of 268 chronic hepatitis C patients (31 chronic persistent hepatitis CPH, 69 mild chronic active hepatitis CAH, 125 severe CAH, and 43 active cirrhosis) enrolled from 1988 to 1991 in different therapeutic protocols using lymphoblastoid or recombinant interferon (IFN) at a dosage of 3 mega units (M.U.), three times a week for 12 months. Of these patients 54.8% showed a complete response (normalization of aminotransferases), 14.2% a partial response (decrease in aminotransferases of over 50%), 27.6% no response, and 3.4% a substantial progressive increase in the liver enzymes during IFN (becoming worse). The prevalence of non responders was lower in CPH (9.7%) than in CAH patients (31.9% in the mild form and 20.8% in the severe), and significantly higher in patients with cirrhosis (53.5%). No correlation was observed between non response and the baseline aminotransferase level or the patient's sex. Patients under 35 had a better response to IFN when compared with patients 36-50 years. This is probably due to the higher prevalence of CPH patients with a good response to IFN in the youngest group. No effect was gained in non responders by increasing the dose or shifting from recombinant to lymphoblastoid IFN; three patients were then treated with steroids, but only one benefitted. For 5 of the 9 patients who became worse, steroids were started after discontinuation of IFN therapy, and they induced a favorable response only for the 3 who had developed autoantibodies during IFN treatment.