We tested the hypothesis that Apgar scores are in part related to the newborn infant's level of maturity. Seventy-three pregnant women with normal fetuses of gestational age 22 to 42 weeks were studied. Fetal well-being was documented by a prospectively designed recording of pregnancy history, labor complications, and birth outcome, including cord blood pH and base deficit measurements. The 1- and 5-minute Apgar scores were directly related to gestational age. Respiratory efforts, muscle tone, and reflex were the major determinants for a decreasing Apgar score with declining gestational age. We conclude that the 1- and 5-minute Apgar scores are influenced by the infant's level of maturity and that our data may be useful in evaluating the true value of Apgar scores in assessing the fetal and neonatal condition of low birth weight infants.