OBJECTIVE: Hepatitis B virus (HBV) precore mutant infection is associated with a more severe liver disease and a poorer response to interferon. We evaluated the efficacy and tolerance of lamivudine to induce complete and sustained suppression of viral replication in seven patients infected with HBV precore mutant (HBeAg-/HBeAb+/HBV DNA+) (in three patients mutation at codon 1896 was detected by direct sequencing). METHODS: Of the seven patients, five had decompensated HBV cirrhosis in a replicative phase and were liver transplant candidates (Group A) and two patients underwent orthotopic liver transplantation (OLT) for HBV liver cirrhosis and developed recurrent HBV infection in the grafted liver (Group B). Lamivudine 100 mg daily was administered orally for a period of 6-75 wk. RESULTS: After 6-8 wk lamivudine therapy was well tolerated and successfully suppressed HBV replication to an undetectable serum level of HBV DNA by polymerase chain reaction in six patients. In Group A, two patients underwent successful OLT with no evidence of HBV reinfection 2-14 months later. Lamivudine was continued after OLT with no episodes of rejection. Three patients died before a suitable liver could be found (one remained serum HBV DNA+ after 6 wk of lamivudine therapy). In Group B, 9-14 months after lamivudine therapy both patients developed lamivudine resistance (increased liver enzymes, reappearance of serum HBsAg and HBV DNA [by hybridization]). In both patients liver histology had progressed and in both, mutation at codon 552 of the HBV polymerase gene was detected. CONCLUSIONS: Lamivudine is well tolerated in patients with decompensated liver cirrhosis due to HBV precore mutant infection who are liver transplant candidates. In four patients (80%) potent suppression of viral replication was detected, allowing OLT to be performed. However, post-OLT, a resistant mutant developed under lamivudine therapy. Combination therapy with other antiviral agents should be evaluated to discourage the emergence of lamivudine-resistant mutants.