Seventy-seven consecutive HBeAg-positive chronic hepatitis patients were studied from 1971 to 1983 to establish the seroconversion rate in the e system. Patients with less than a year of follow-up were not included in the study. Fifty-six patients with chronic active hepatitis (CAH) received immunosuppressive treatment (corticosteroids combined with azathioprine). The remaining twenty-one patients received no treatment, nine of them with chronic persistent hepatitis (CPH) and 12 with CAH. A retrospective study was performed with stored sera samples: HBeAg and anti-HBe were determined by RIA, and results were correlated with alanine aminotransferase (ALAT) levels in the same samples. The linearized seroconversion rate from HBeAg to anti-HBe was expressed as percent per patient-year. It was 9.6% in CPH patients and 8.8% in CAH patients without treatment. In CAH patients under immunosuppressive drugs it was as low as 1.1% and increased to 28.7% when treatment was withdrawn. ALAT levels were significantly lower in total seroconverted patients when compared with nonseroconverted (NS) patients, but no difference was found between partial seroconverted (PS) and NS patients. The results suggest that although immunosuppressive drug withdrawal may enhance seroconversion rate in type B CAH, delayed seroconversion and reported side effects during treatment stand against protracted usage of these drugs.