The binding activity of polymerized human serum albumin to the receptor on hepatitis B virus (HBV-pAR activity) was examined in relation to the evolution of the HBeAg/anti-HBe system in sera from symptom-free carriers and patients by the use of an enzyme-linked immunosorbent assay (ELISA). The sera of 80 HBsAg-positive symptom-free students (18～20 years old) and of 2 patients with severe chronic active hepatitis (CAH 2B) followed up for 3 years were used. The students were divided into 2 groups: 3 cases of horizontal infection (group 1) and 77 cases of maternal infection (group 2). The students of group 1 initially showed positive HBeAg and high HBV-pAR activity, but showed positive anti-HBe and low HBV-pAR activity after a typical course of acute hepatitis. In group 2, 35 (45.5%) of the 77 students showed initially positive HBeAg, and all except one student had hgih HBV-pAR activity. Ten of the 34 students with both positive HBeAg and high HBV-pAR activity had abnormal S-GPT levels in the 3-year follow-up period. Six of the 10 students became symptom-free with negative HBeAg and low HBV-pAR activity, and two students showed positive anti-HBe. Four students developed middle HBV-pAR activity and had persistent abnormal S-GPT levels. Twenty-four (68.6%) of the 35 students with positive HBeAg did not undergo serocon-version. One student with positive HBeAg and low HBV-pAR activity became symptom-free with negative HBeAg and negative anti-HBe without abnormal S-GPT levels. The two HBsAg, HBeAg-positive patients with CAH 2B had an acute exacerbation, and showed high HBV-pAR activity 1~2 months before the exacerbation. One of them became symptom-free with negative HBeAg and low HBV-pAR activity, but the other became symptom-free with positive HBeAg and low HBV-pAR activity after the exacerbation. The results indicate that HBV-pAR activity might be a more useful marker for determining the prognosis of HBsAg-positive students than HBeAg/anti-HBe.