The purpose of this study is to compare a combination of interferon (IFN)-alpha2a (Roferon) + Tenoxicam with IFN-alpha2a alone in the treatment of chronic hepatitis C. This prospective, randomized double-blind study included 149 patients, all of whom were diagnosed with active chronic hepatitis C but non-cirrhotic (ALT > or = 1.5 upper limit of normal, anti-hepatitis C virus (HCV) positive by enzyme-linked immunosorbant assay2 and RIBA3). The patients were randomized in two groups, as follows: G1 (n = 76): IFNalpha2a 3 million units times per week during 6 months + placebo; and G2 (n = 73): IFNalpha2a 3 million units three times per week + Tenoxicam (20 mg/day) during 6 months. Alanine aminotransferase (ALT) and HCV RNA were determined before and at months 6 and 12 of treatment. 2'5' oligoadenylate synthetase activity (2'5' AS) was dosed in mononuclear cells before and at 3-month treatment intervals in 28 patients. Liver biopsy was performed before and 6 months after the end of therapy. Parameters were similar before therapy for both groups. Biochemical and virological responses were similar for both groups at month 6 (49.3% vs. 42.9% and 43.3% vs. 38.3%, respectively) and month 12 (28.3% vs. 23.8% and 17.2% vs. 17.5%, respectively). HCV RNA level significantly decreased in both groups at month 6, with no difference whatever the therapy; however, the HCV RNA level returned to initial values at month 12 and was the only significant prognostic factor of a sustained response. No peak of 2'5' AS activity was observed during treatment in patients with dual therapy. A histological improvement was also noted in both groups without difference, regardless of therapy. The percentage of adverse events was identical for both groups. Paracetamol intake, assessed in 80 patients, was 49.1 g per 6 months in the G1 group and 22.5 g per 6 months in the G2 group (not significant). In conclusion, the non-steroid anti-inflammatory drug, Tenoxicam, does not increase IFNalpha efficacy in the treatment of chronic hepatitis C. This combination is well tolerated and partially lowers Paracetamol intake, but not preexisting alpha-IFN adverse events.