One-hundred sixty patients (81 cyanidanol, 79 placebo) were included in a double-blind placebo-controlled clinical trial to evaluate the effect of 3 gm (+)-cyanidanol-3 per day for 8 weeks on the clinical course of acute viral hepatitis and HBsAg elimination. Quantitative determination of HBsAg was performed at frequent intervals. The mean time for serum bilirubin to decrease to 1.3 mg per dl was 30.8 +/- 3.5 days in the treated group and 52.2 +/- 9.8 days in the control group, (p less than 0.025). The time for SGOT to decrease to 100 IU per liter was 17.98 +/- 1.82 in the treated group and 26.53 +/- 3.7 in the control group (p less than 0.025). No significant difference in the evolution of other laboratory values or symptoms was found. The elimination rate of HBsAg was identical in both groups. Treatment did not alter the incidence of chronicity.