AbstractSera from four patients with acute hepatitis B and 87 patients with chronic hepatitis B were examined quantitatively for pre‐S1 and pre‐S2 antigens by solid‐phase enzyme immunoassays. Pre‐S1 and pre‐S2 antigens were detected in HBsAg‐positive sera irrespective of the presence of viral replicative markers, and their titers correlated with those of HbsAg(r = 0.74, p<0.01; r = 0.74, p<0.01, respectively). Sera positive for HBeAg showed higher titers of pre‐S1 (p<0.01) and pre‐S2 (p<0.01) antigens than sera negative for HBeAg. The titers of pre‐S1 and pre‐S2 antigens also correlated with the levels of HBV‐associated DNA polymerase activity (r = 0.51, p<0.01; r = 0.59, p<0.01, respectively) and HBV‐DNA (r = 0.50, p<0.01; r = 0.46, p<0.01, respectively). However, the ratios between the titers of pre‐S antigens and HBsAg had no significant relationships with those viral replicative markers. These findings suggest that the expression of pre‐S antigens is intimately related to the expression of HBsAg and that they are not useful as markers of viral replication. The ratios between the titers of pre‐S antigens and HBsAg tended to be high in patients with chronic active hepatitis and high aminotransferase levels. This finding may have been due to the hepatic release of pre‐S antigens, overproduction of which may have so