OBJECTIVE As previous studies have shown a good response of mixed cryoglobulinemia (MC) to alpha-interferon (IFN) therapy, we investigated the efficacy and tolerability of two IFN regimens in a group of 36 patients affected by MC. METHODS The patients, diagnosed on the basis of standard clinical and laboratory criteria, were randomly divided into 2 groups: group A (18 cases) received alpha 2b-IFN 3 M.U. thrice a week for six months, while group B (18 cases) received alpha 2b-IFN thrice a week for 1 year. The patients were followed for six months after the end of therapy. Liver function tests, cryoglobulin determinations and a clinical examination were performed each month. HCV serology and HCV-RNA detection by PCR were performed before therapy and at the end of the follow-up period. RESULTS The two study groups were comparable in age, male/female ratio, purpura score, cryoglobulin level, mean ALT serum activity and liver histology. 32 patients (89%) were positive for anti-HCV antibodies and 29 (81%) for HCV-RNA. During therapy all patients showed a significant (p < 0.001) decrease in their cryoglobulin level as well as improvement (p < 0.05) in their purpura score. In group A, five patients (28%) showed normalized ALT, but three later relapsed. In group B seven patients (39%) responded to treatment but three relapsed after suspension of the drug. Two patients from group B developed severe side effects (hypothyroidism and depression) and therapy was discontinued after 9 and 11 months, respectively. In all the non-responders and relapsed patients, purpura, ALT, and cryoglobulins rose to pre-treatment levels within a few months. At the end of follow-up, two patients from group A (11%) and four in group B (22%) had achieved complete remission. CONCLUSIONS This study indicates that IFN is useful in MC and that viral replication can be considered the target of the therapy. Despite the absence of a statistical difference in the response rate between the two regimens (due to the low number of subjects), the one-year therapy course seemed to show a better efficacy, although associated with higher toxicity.