One hundred and forty-eight patients with non-alcoholic cirrhosis or chronic aggressive hepatitis entered a prospective, unblinded, randomized trial on the effect of azathioprine versus prednisone. For all 148 patients, there were no differences in survival related to the two drugs. In 99 patients the disease was classified as autoimmune, in 23 as posthepatitic, and in 26 as cryptogenic. No significant differences were seen in survival between these three groups of patients and no differences in survival related to the two drugs were registered within any of the groups. The autoimmune group included the patients with the biochemically most active disease, and a statistically significant reduction in activity was obtained with prednisone as well as azathioprine. Most remarkably, the frequencies of the autoantibodies were reduced parallel to the biochemical improvement in these patients. Immunosuppressive treatment was found to be rather ineffective in posthepatic chronic liver disease of type B; however, no signs of activation of the hepatitis B virus were seen.