AIM To characterize effects of interferon alpha (If-a) on functional activity of platelets in patients with chronic viral hepatitis (CVH) and viral hepatic cirrhosis (VHC). MATERIAL AND METHODS Induced platelet aggregation (PA), spontaneous PA, levels of cAMP, cGMP and glycogen in platelets, plasm beta-thromboglobulin (bTG) and activity of thrombocytic factor 4 (TF4) were measured in 95 patients before, 4.5 h after the first If-a introduction, after 12 and 24 weeks of If-a treatment. RESULTS The patients demonstrated low induced PA, intracellular glycogen and high cAMP, b-TG and TF4. The initial administration of If-a led to normalization of most of functional platelet indices. A 24-h course of If-a therapy normalized platelet functions irrespective of stability of the virusological response. CONCLUSION If-a preparations in single and multiple administrations normalize platelet function.