In the present study, we have analyzed the amount of precore wild-type hepatitis B virus (HBV) (wild-type) and precore mutant HBV (nt 1896: G --> A) (precore mutant) of HBV carriers; 31 asymptomatic healthy carriers (ASC) and 28 patients with chronic hepatitis (CH). Wild-type and precore mutant were quantified using sensitive and specific quantification methods: competitive wild-type-sequence-specific assay and competitive mutation-site-specific assay with different sets of specific primers and internal controls. Median serum levels of wild-type and precore mutant were 9.60 and 8.60 log copies/ml (median percentages of precore mutant in total HBV-DNA: 11.7%) in HBeAg(+) ASC, 8.48 and 8.00 (33.3%) in HBeAg(+) CH, and 6.30 and 6.85 (84.7%) in anti-HBe(+) CH, respectively, showing higher levels of the relative amount of precore mutant to wild-type along with HBeAg/anti-HBe status. Only precore Mutant, but not wild-type was detected in anti-HBe(+) ASC. Although median percentages of precore mutant at the anti-HBe(+) ASC and CH stages were much higher than those at the HBeAg(+) ASC and CH stages, a Substantial amount of precore mutant was found even at the HBeAg(+) stages. Existence of a substantial amount of precore mutant even in HBeAg(+) ASC suggests that the occurrence of precore mutant is not always closely associated with seroconversion from HBeAg to anti-HBe. (C) 2002 Elsevier Science B.V. All rights reserved.