Five patients presenting with HBs Ag and HBe Ag-positive chronic hepatitis were treated with adenosine arabinoside (Vidarabine) in doses of 15 mg/kg/day. The drug was administered by intravenous infusion in 2 series of 5 infusions each separated by 2-day intervals. Two patients had a second course 4 months after the first one. There were no clinical or biochemical adverse reactions. Following treatment, serum transaminase levels returned to normal. All patients became HB Ag-negative, with presence of anti-HBe antibody in three; two patients became HBs Ag-negative, with presence of anti-HBs antibody in one. Although very short, this series should encourage further therapeutic studies, including a controlled, randomized trial in a large number of patients.