A prospective double-blind controlled study was performed on the effects of isoprinosine in 81 patients with clinical and histological features of classical acute viral hepatitis. Appetite was assessed daily. Serum alanine aminotransferase, aspartic aminotransferase, and bilirubin levels were assessed weekly. Changes in biochemical parameters, number of deaths, number of patients showing rise of aminotransferase levels despite treatment, and duration required for appetite to return to normal in each group were compared. Observation was continued for 4 weeks. Contrary to preliminary reports, no therapeutic benefit was demonstrated in any of these parameters. We concluded that isoprinosine was ineffective in the acute phase of classical acute viral hepatitis.