Sera obtained from asymptomatic HBV carriers (ASC, n=227), chronic hepatitis B (CH, n=31, pretreatment), or CH receiving liver biopsies before and after IFN (n=15) were examined for the deletions in the pre-S region of HBV. The results were expressed as percent positive for deletions in Pre-S1/-S2. 1) Stages: 0%/0% detected in HBeAg+ve ASC, 21%/24% in HBeAg+ve CH, 14%/19% in HBeAg-ve CH, and 11%/7% in HBeAg-ve ASC. 2) HBeAg+ve CH patients: a) ages; 21%/9% detected in HBeAg+ve CH with less than 30yo, 21%/35% in HBeAg+ve CH with more than 30yo. b) Disappearance of HBeAg was observed in 24%/4% of those with deletion, 11%/17% without deletion. c) Pretreatment; 29%/0% detected in both liver and serum, 36%/86% in neither liver or serum, 0%/7% in serum only, and 36%/7% in the liver only. d) Post-treatment; Deletions disappeared in 25%/0% in serum and in 71%/0% the in liver. The results suggest that the deletions in pre-S region result from chronic inflammation. Disappearance in HBeAg with IFN treatment accompanied more frequently pre-S1 deletion than pre-S2 deletion.