Prenatal alpha-fetoprotein screening may serve as an index of suspicion of many congenital anomalies of the fetus including neural tube defect and aneuploid fetus. This study was undertaken to determine the normal ranges of AFP in maternal serum and amniotic fluid at 9 to 41 weeks gestation which thus far had not been established in Korea. Normal ranges of maternal serum and amniotic fluid AFP from 9 to 34 weeks and from 16 to 41 weeks gestation were obtained respectively from 198 uncomplicated pregnant women delivered of normal singleton baby. Maternal serum AFP values showed an increasing trend from 12 weeks gestation reaching a peak level at 29 to 34 weeks gestation and after which there was a gradual decline. Amniotic fluid AFP values was the highest at 17 weeks gestation and declined as pregnancy approached term. The correlation of a median value between AF AFP and MS AFP was 100 to 1 in ratio in each week. The authors conclude that this initial experience in Korea with maternal serum AFP values could efficiently detect genetic disorders, perhaps with high sensitivity and provide a proper management scheme of pregnant women with abnormal high and low AFP values during the midtrimester of pregnancy.