To define the relationship between pre-core hepatitis B virus mutants and the long-term outcome of chronic hepatitis B virus infection, we monitored the type of circulating pre-core hepatitis B virus-DNA by polymerase chain reaction and sequencing in 41 selected chronic HBsAg carriers with extensive follow up. They included 12 HBeAg-positive patients with chronic hepatitis, who seroconverted to anti-HBe during follow up and 29 anti-HBe positive patients, 23 of whom had chronic hepatitis and six acute severe exacerbation occurring spontaneously (three cases) or during antitumor chemotherapy (three cases). In the presence of HBeAg, all showed prevalence of the pre-core wild type along with high levels of viral replication and elevated alanine aminotransferase. Anti-HBe seroconversion was accompanied by a dramatic reduction of hepatitis B virus replication and normalization of alanine aminotransferase in all, except one, and by the emergence of mutated strains with a pre-core stop codon (point mutation G to A at nt 1896) that replaced the wild type in seven of the 12. Of the seven who harboured the pre-core mutant, three continued to show normal alanine aminotransferase during subsequent follow up, three had mild alanine aminotransferase elevation and one had an acute short-lived reactivation after 4.4 years of normal alanine aminotransferase. The five cases who continued to show prevalence of wild type in spite of anti-HBe seroconversion all revealed persistently normal alanine aminotransferase.(ABSTRACT TRUNCATED AT 250 WORDS)