This study reports clinical, serological and immunomorphological observations on viral hepatitis in 14 HBsAg-positive renal transplanted patients treated with cyclosporin and steroids. Eleven patients who were HBsAg positive before transplantation developed signs of hepatitis. This was due to HBV in six cases and progressed into a mild chronic disease. The remaining five subjects lacked signs of HBV reactivation. The hepatitis, attributed to non-A non-B agents, recovered completely. Two more patients became HBsAg positive after transplantation both developed acute hepatitis, respectively drug and HBV related. Transition into chronicity occurred only in the latter case. The results seem to indicate: (1) the possibility of a high incidence of non-B virus hepatitis in HBsAg-positive transplanted patients under cyclosporin treatment; (2) a good prognosis in non-B hepatitis as compared to hepatitis B for the same patient group; and (3) a mild degree of disease activity in cases who develop chronic hepatitis.