The effect of prednisone (15 mg/day) or azathioprine (2 mg/kg daily) or a combination of prednisone (10 mg/day) and azathioprine (2 mg/kg daily) was assessed in a controlled multi-centre trial of chronic-active hepatitis. Since 1st January, 1972, a total of 162 patients were registered, 81 previously untreated. Fifty-two of them (30 HBs-antigen negative and 22 positive) fulfilled the criteria for admission to the treatment trial. 27 of 29 patients not fulfilling the criteria had HBs-antigen positive chronic-active hepatitis. All 29 untreated patients had slight active non-progressive chronic-active hepatitis over an observation period of one to four years by clinical, biochemical and histological criteria. Taking into account clinical, biochemical and histological findings, a treatment effect independent of treatment form was noted in 23 of 30 of the HBs-antigen negative patients. In 18 of the 23 successfully treated patients auto-antibodies were demonstrable. In contrast, in 18 of 22 patients with HBs-antigen positive chronic-active hepatitis no objective improvement or influence on the clinical course was observed, independent of form of treatment, and three died. It is concluded that HBs-antigen negative, auto-antibody positive chronic-active hepatitis is an indication for immunosuppressive treatment with prednisone or azathioprine or the two combined.