21 patients with chronic active hepatitis B (CAH-B) were treated for 1-2 years with isoprinosine, while another 18 patients served as control group. All patients were initially DNA polymerase (DNAp) and HBeAg positive. Nine (43%) treated patients became persistently negative for DNAp, seroconverted to anti-HBe and showed histological remission on follow-up biopsy. Among simultaneously followed controls 5 (28%) lost DNAp and 4 (22%) also lost their HBeAg. However, only 2 (11%) seroconverted to anti-HBe. Histological improvement was seen in 5 (28%) controls. Thus, it seems that isoprinosine may exert a beneficial effect on the course and outcome of CAH-B.