To elucidate the effects of pregnancy and delivery on hepatitis B e antigen (HBeAg)-positive carrier mothers, 31 HBeAg-positive carrier mothers were followed-up postpartum 1 year, with 30 HBeAg-positive nonpregnant female carriers as controls. Serum hepatitis B surface antigen (HBsAg), HBeAg titer, and hepatitis B virus (HBV)-DNA concentration were studied at defined intervals. The results revealed that in the control group HBeAg titers and HBV-DNA concentrations fluctuated, whereas the HBsAg titers showed little change, but HBeAg clearance or seroconversion to anti-HBe were not noted on follow-up. In contrast, one carrier mother seroconverted to anti-HBe during pregnancy and the antibody persisted thereafter. Five of the remaining 30 carrier mothers cleared HBeAg postpartum, and among these five cases, one also seroconverted to anti-HBe. In addition, in another five of the 30 cases, the HBV-DNA fell to undetectable level (less than 0.04 ng/ml). All these ten cases had a common tendency of showing a decrease in HBeAg titers and/or HBV-DNA concentrations 1-2 months after delivery. The HBeAg titers and HBV-DNA concentrations in the other 11 cases remained unchanged, whereas the remaining nine cases had increased levels. It is concluded that subsidence of HBV replication is precipitated by delivery in one-third of HBeAg-positive carrier mothers in Taiwan, and this occurs most frequently 1-2 months postpartum.