Accuracy of prediction of fetal maturity as judged creatinine concentrations and fat cell counts in the amniotic fluid, the anterior wall length of the gravid uterus and the abdominal circumference of pregnant women were studied. In this study 37 weeks of gestation and 2,500 gm. of birth weight were considered to be the lower limits of mature infant. When 37 weeks of gestation was chosen as a criterion of lower limits of fetal maturity, accuracy of prediction in the mature group as judged by creatinine concentration, fat cell counts, lenght of anterior uterine wall, abdominal circumference of pregnant women were 93.3%, 86.5%, 84.3%, 85.3% respectively. In premature group the results were 75.0%, 81.3%, 75.0%, 62.5% respectively and over all results were 90.5%, 85.7%, 82.9%, 81.9% respectively. On the other hand if birth weight of 2,500 gm. is chosen as criterion of lower limit of fetal maturity, accuracy of prediction in the mature group as judged by creatinine concentration, fat cell counts, length of the anterior uterine wall, abdominal circumference of the pregnant women were 92.1%, 87.6%, 86.5%, 82.0% respectively. In premature group the results were 75.0%, 87.5%, 68.8%, 75.0% respectively. In premature group the results were 75.0%, 87.5%, 68.8%, 75.0% respectively, and over all results were 89.5%, 87.6%, 83.8%, 81.0% respectively.