There were 25-1 cases studied in which two tests of fetal maturity were performed within 72 hours of each other. The two tests were an x-ray fetogram and an amniotic fluid L/S ratio determination. All fetograms were read by one author for the presence of distal femoral epiphysis (DFE). It was assumed that DFE permits estimation of fetal hone maturation and L/S ratio permits estimation of fetal lung maturity. The DFE results gave a 10% false positive rate in predicting a mature L/S ratio (>2.0) and a 38.7% false-negative rate. Of the 21 patients who delivered within 3 days of the performance of the two tests, all neonates did well when there were no visible DFE's hut a mature L/S ratio. There is a significant lack of specificity and sensitivity of the fetogram DFE is in predicting a mature L/S ratio. Since infant lung maturation is a critical factor in predicting neonatal survival, these results suggest that the x-ray DFE is unacceptable as a single maturity test for use in a perinatal center managing complicated obstetric cases.