During a follow-up period of 3.2 ± 1.6 (1 to 8.6) yr, 1,087 serum specimens from 230 HBsAg carrier children were tested for hepatitis B virus markers. Dividing the serum specimens into four groups according to the status of HBeAg and hepatitis B virus DNA, the frequency of abnormally elevated ALT levels in serum was in the following order: HBeAg(+)/hepatitis B virus DNA(−) serum (60%), HBeAg(−)/hepatitis B virus DNA(+) serum (53%), HBeAg(+)/hepatitis B virus DNA(+) serum (41%), HBeAg(−)/hepatitis B virus DNA(−) serum (11%). Analysis of the data before HBeAg clearance showed that both a high serum ALT level and a low serum hepatitis B virus DNA level correlated with an imminent clearance of HBeAg. Approximately two thirds of children with serum ALT levels higher than 100 IU/L cleared HBeAg within the following year. Clearance of HBeAg occurred within the following year in 65% (13 of 20) of cases with serum hepatitis B virus DNA level ≤ 1,000 pg/ml, in contrast to 19% (30 of 157) of those with serum hepatitis B virus DNA level > 1,000 pg/ml. Among 53 children who lost HBeAg and hepatitis B virus DNA during follow-up, only nine cases did not have an identified period of abnormal serum ALT levels. For the remaining 44 children, abnormal serum ALT levels fell to normal with clearance of both HBeAg and hepatitis B virus DNA in 33 children but remained elevated in the remaining 11 cases after seroconversion. This study also demonstrated that (a) serum ALT elevations in HBsAg carrier children were usually mild in degree and infrequently exceeded 100 IU/L, (b) hepatitis B virus DNA was detectable in only 1% (4 of 352) of the anti-HBe(+) sera and all showed normal ALT levels. These findings are in contrast to the adult carriers and denote some unique features of HBsAg carrier children. (HEPATOLOGY 1990;12:657–660).