The persistence of Hepatitis B surface antigen (HBsAg) in 156 patients with histopathologically proven acute viral hepatitis and 27 patients with chronic active hepatitis was assessed and correlated with their clinical and histopathological outcome; 1387 sequential serum samples were tested for HBsAg and its antibody (anti HBs). In the group with acute viral hepatitis, 86% of the patients who recovered, 67% of the patients who deteriorated histopathologically and 67% of the fatal cases carried HBsAg for up to 8 weeks only. While 56% of patients with chronic active hepatitis harboured HBsAg for 13-80 weeks, only 10% of the group with acute viral hepatitis did so. Of patients with chronic active hepatitis 37% deteriorated to cirrhosis and 11% died. Diverse anti-HBs-response patterns are reported and may have clinical significance.