Among 95 term infants with benzoylecgonine, the cocaine metabolite, detectable in their meconium, there was an inverse relation between the concentration of benzoylecgonine and birth weight, length, and head circumference. Multiple regression analysis confirmed these relations after controlling for gestational age and maternal use of marijuana, cigarettes, and alcohol. These data suggest a dose-response relation between the magnitude of prenatal cocaine exposure and impaired fetal growth.