To evaluate the status of hepatitis B virus infection in the mothers and neonates and to determine the maternal-neonatal transmission of hepatitis B virus, 2,276 term pregnant women were screened for presence of serum HBsAg, at the Department of Obstetrics and Gynecology, Yeungnam University Hospital, during the period of 18 months from Jan. 1986 to Jun. 1987, and the sera of sixty-six HBsAg carrier mothers and their neonates were tested for HBV markers and liver enzymes. The results were as follows: 1. The prevalence rate of asymptomatic HBsAg carrier in the term pregnant women was 4.7% (53/1,279). 2. Positive rates of HBsAg and anti-HBs in the sera of sixty-six neonates born to asymptomatic HBsAg carrier mothers were 12.1% and 9.1%, respectively. Transient elevation of SGOT (three to four times of upper normal limit) was detected in one of eight HBsAg-positive neonates and one of six anti-HBs positive neonates. 3. Positive rates of anti-HBc, HBeAg and anti-HBe in the sera of sixty-six asymptomatic HBsAg carrier term pregnant women were 93.9%, 45.5%, 50%, respectively. The rates of transmission of maternal anti-HBc, HBeAg and anti-HBe to the neonates were 85.5 (53/62), 90% (27/30) and 87.9% (29/33), respectively. 4. Serum HBsAg was detected in four of thirty neonates born to HBeAg positive HBsAg carrier mother, three of thirty-three neonates born to anti-HBe positive HBsAg carrier mothers, and one of three neonates born to both HBeAg and anti-HBe negative HBsAg carrier mothers.