Blood Spot 17 alpha-hydroxyprogesterone (17-OHP) concentrations in neonates, especially in premature babies, were determined in relation to 1) the gestational age at birth, 2) the equivalent age of gestation at blood sampling and 3) the birth weight. The 17-OHP concentrations were found to be higher with prematurity. Accordingly, the cut-off limit in screening for congenital adrenal hyperplasia (CAH) in premature infants is proposed as 20 ng/ml. Ideal cut-off limits were set by the equivalent age of gestation at blood sampling. Cut-off limits on the basis of gestational age at birth and birth weight are also suggested, where the sampling age is not so advanced. The rate of false positivity in premature infants can be reduced by this method.