PURPOSE: We studied prevention effects of vertical transmission of Hepatitis B with follow-up, through the change of Anti-HBs titers during 9 months after injection of Hepatitis B immunoglobulin (HBIG) and Hepatitis B vaccine (HBV) at birth in newborn delivered from Hepatitis antigen carrier mothers. METHODS: This study was performed on newborn delivered from HBsAg carrier mothers at Hae Sung Hospital from Feb. 1995 to May 1996. These newborn were injected intramuscularly with HBV and HBIG after evaluation of HBsAg and Anti-HBs titer directly at birth. Regular Hepatitis vaccination was given at 1 month, 6 months as well as HBsAg and Anti-HBs titer were evaluated at 24 hours, 1 month, 3 months, 6 months, and 9 months. RESULTS: The incidence of Hepatitis B carrier mothers is 5.6%, and newborn babies born to HBsAg carrier mothers showed HBsAg in 10.6%. In most newborn, Anti-HBs titer maintained in 100-1,000mIU/ml after injection of HBIG and HBV at birth, and mean Anti-HBs titer decreased a little at 1 month, but therafter increased gradually by regular Hepatitis vaccination. HBsAg positive newborn maintained mean HBsAg titers below 2 (S/N) until 9 months old after injection of HBIG and HBV. CONCLUSIONS: A screening test for Hepatitis B must be performed on all pregnant women, and that infants of Hepatitis B carrier mothers must be immunized by HBIG and HBV directly at birth.