The age-specific prevalence of hepatitis B e antigen (HBeAg) and its antibody (anti-HBe) were studied by radioimmunoassay, and compared in a large series of patients with chronic hepatitis B virus (HBV) infection, including 268 asymptomatic carriers, 389 chronic hepatitis, 114 liver cirrhosis, and 278 hepatocellular carcinoma (HCC). The prevalence of HBeAg/anti-HBe in asymptomatic carriers and patients with chronic hepatitis correlated closely with age as HBeAg prevalence decreased and anti-HBe prevalence increased with increasing age (P less than 0.0005), and is probably due to high infection rate at young age in Taiwan. The prevalence of HBeAg in patients with both cirrhosis and HCC are much significantly lower and had no correlation with age. Two peaks of age-specific prevalence of HBeAg and anti-HBe were observed in patients with HCC, implicating two patterns of HBV infection in these patients. The difference in the prevalence of HBeAg and anti-HBe might indicate that asymptomatic carriers, chronic hepatitis, liver cirrhosis, and HCC are sequential sequelae of HBV infection.