Two hundred and twenty two asymptomatic carriers of hepatis B surface antigen (HBsAg) with age between 4 months and 68 years, 172 healthy persons with antibody to HBsAg (anti-HBs) and 85 healthy persons seronegative for both HBsAg and anti-HBs were studied by double immunodiffusion for the evaluation of the meaning of hepatitis B e antigen (HBeAg) and its antibody (anti-HBe). In 222 asymptomatic carriers, HBeAg was detected in 32.4% and anti-HBe in 31.5%. The geometric titer of HBsAg was 1:2159 in the HBeAg positive and 1:149 in the anti-HBe positive persons. Frequencies of HBeAg and anti-HBe in asymptomatic carriers of HBsAg correlated closely with age. The highest frequency of HBeAg was found in the first decade in 64% decreasing steadily to 20.8% in the fourth and then suddenly down to 4.1% in the fifth decade. A reverse trend was observed in anti-HBe frequency. From our analysis, it is likely that the high frequency of HBeAg in serum of Chinese, especially in females of fertile age, might be an important contributing factor for the high rates of hepatitis B virus (HBV) infection and HBsAg carrier in Taiwan. The presence of HBeAg/anti-HBe system is not only a market of infectivity and prognosis but also a chronologic marker of HBV infection.