Hair analysis for the major metabolite of cocaine, benzoylecgonine (BZE) was performed in a cohort of 251 predominantly African-American newborns utilizing a modified radioimmunoassay (RIA) (Abuscreen Roche Laboratories, Nutley, N.J., USA). Maternal drug intake was confirmed by positive urine drug screen for cocaine metabolites at the time of delivery. The BZE concentrations reported here are the composites of both the parent compound cocaine (hydrolyzed to BZE) and the native BZE metabolized by the patient and deposited in the hair follicle. Hair analysis as an indicator for gestational cocaine exposure had a sensitivity of 88%, specificity of 100%, positive predictive value of 100%, and negative predictive value of 85%. The range of BZE was 99–23,300 ng/g of hair, with 79% having hair BZE levels <5,000 ng/g of hair. The BZE RIA was confirmed by gas chromatography and mass spectrometry (GC/MS). Of the 18 mother/infant pairs tested, the hair BZE ratio (maternal to neonatal) varied from 0.5 to 8.9 in 13 pairs. In spite of maternal high hair BZE levels, 5 newborns had no evidence of hair BZE, stressing the importance of the placental role for the cocaine transfer to the fetus. After controlling for gestational age, higher BZE levels significantly correlated with smaller head circumference (p < 0.03) and birth weight (p < 0.01).