The Brazelton Neonatal Behavioral Assessment Scale was administered to 54 term, healthy infants on days 1, 2, 3, 4, 5, 7, and 10. Infants were divided into 8 groups of maternal obstetrical medication. A separate drug factor score was computed from 4 variables: time from (1) first and (2) last drug administration to delivery, (3) number of different drugs, and (4) drug administrations. In order to determine the additive effects of drug and other obstetric factors on neonatal behavior, the drug group and drug factor score plus length of labor, parity, and the ponderal index were used in a series of multiple regression analyses to predict Brazelton scale cluster scores on each day. In a second set of multiple regressions, these variables were used to predict the infant's rate of behavioral change as estimated by the slopes of the Brazelton scale cluster scores across the 7 days. The results indicated that the combined effect of the predictor variables significantly explained 10%-28% of the variance in neonatal behavior. It was hypothesized that the effects of low levels of medication are subtle but may be unmasked when medication effects are studied in combination with other factors that may potentiate drug effects.