OBJECTIVES: Treatment with pegylated interferon (PEG-IFN) alpha-2b results in hepatitis B e antigen (HBeAg) loss in 36% of patients at 6 months post treatment. The aim of this study was to determine whether a long-term response to PEG-IFN is dependent on the timing of HBeAg loss. METHODS: A total of 91 patients treated with PEG-IFN alpha-2b alone (100 mu g per week) and 81 patients treated with PEG-IFN alpha-2b and lamivudine (100 mg/day) for 52 weeks were enrolled in this study. Patients were initially followed up at 4-week intervals and had one additional long-term follow-up (LTFU) visit (mean: 3.03 +/- 0.77 years 26 weeks post treatment). RESULTS: Of the 172 patients included, 78 patients (46%) did not have loss of HBeAg, 47 (27%) lost HBeAg within 32 weeks, and 47 patients (27%) had loss of HBeAg after week 32. At LTFU, patients with HBeAg loss <= 32 weeks had hepatitis B virus DNA of <400 copies/ml significantly more often than did those who lost HBeAg after week 32 (47 vs. 21%, respectively; P=0.009). Hepatitis B surface antigen (HBsAg) negativity was also observed significantly more often in patients with early HBeAg loss (36 vs. 4%, respectively, P<0.001). Early HBeAg loss tended to occur more often in patients treated with PEG-IFN and lamivudine combination therapy than in those treated with PEG-IFN alone (35 vs. 21%; P=0.10), as did HBsAg loss (15 vs. 8%; P=0.14). CONCLUSIONS: Early PEG-IFN-induced HBeAg loss results in a high likelihood of HBsAg loss and may be associated with more profound viral suppression during the first 32 weeks of therapy in patients treated with lamivudine combinations.