In 37 patients with chronic hepatitis B in the stage of active viral replication the authors tried to assess the time of seroconversion of HBeAg to anti-HBe and HBsAg to anti-HBs (21 men, 13 women and 3 boys, mean age of adults 44 years). During the 8-years investigation period seroconversion of HBeAg occurred in 19 of 37 patients (51.3%) which is an annual rate of seroconversion 6.4%. HBeAg disappeared from serum after a mean period of 82 months (range 29-228 months). After seroconversion of HBeAg the ALT and AST activity declined significantly. Acute exacerbation of hepatitis before seroconversion of HBeAg was recorded in 13 of 37 patients (35%). The mean ALT activity at the peak of exacerbation was 7.93 mu kat/l, the average duration of exacerbation was 9.8 months. Seroconversion of HBsAg occurred in 7 of 37 patients (19%). The mean annual rate of seroconversion of HBsAg was 2.4% after an average period of 98 months. During the investigation period 7 patients died (19%), four of them had a constantly positive HBeAg. The authors conclude that very low annual average seroconversion of HBeAg (6.4%) and HBsAg (2.4%) in patients with chronic hepatitis B is probably caused by previous glucocorticoid treatment.