The pathogenesis of the hepatic damage in hepatitis is not well understood but an imbalance in immunoregulatory T lymphocytes is probable. We tested the Theophylline-sensitive T lymphocytes in acute and protracted cases of hepatitis A, in hepatitis B and non-A, non-B. A delayed increment of such cells was demonstrated in hepatitis B suggesting a positive role in the recovery from the disease. The results were indicative for a direct action of the HAV and nAnB on the lymphocytes. Theophylline-sensitive lymphocytes were increased in the course of protracted hepatitis A whereas were progressively decreasing in nAnB hepatitis. This behaviour of suppressor cells in nAnB hepatitis may explain the high frequency of evolution in chronic liver disease.