['To evaluate the usefulness of quantitative hepatitis B surface antigen (HBsAg) and hepatitis B e antigen (HBeAg) for predicting HBeAg seroconversion in chronic hepatitis B patients treated with conventional interferon (IFN) alfa-2b or PegIFN alfa-2b.', 'Fifty-eight patients were enrolled; 29 for the training group and 29 for the validating group. Quantification of HBsAg and HBeAg was carried out at baseline, week 12, week 24, and then again at 12 and 24 weeks follow up, respectively, for two groups. Sixteen patients in the training group were followed up for 5 years.', 'The cutoff of 1500 IU/mL in serum HBsAg at week 12 had a positive predictive value (PPV) of 33% and a negative predictive value (NPV) of 91%, and 2890 IU/mL at week 24 had a PPV of 43% and an NPV of 95% for HBeAg seroconversion at week 48. The cutoff of 17.55 Paul Ehrlich Institute units/mL (PEI-U/mL) in serum HBeAg at week 12 had a PPV of 38% and an NPV of 95%, and 8.52 PEI-U/mL at week 24 had a PPV of 44% and a NPV of 100% for HBeAg seroconversion at week 48. Moreover the HBsAg and HBeAg levels of PegIFN alfa-2b group were lower than those of the conventional IFN alfa-2b group. During follow up, patients with HBeAg seroconversion remained HBeAg negative and none of them progressed to cirrhosis, but among the patients with non-HBeAg seroconversion, two progressed to cirrhosis. Two additional patients with negative HBeAg were observed.'] Are quantitative serum HBsAg and HBeAg strong predictors of sustained HBeAg seroconversion to pegylated interferon alfa-2b in HBeAg-positive patients?