Meconium specimens (first 3 days' stool) obtained from 20 infants of drug-dependent mothers and five control infants were analyzed by radioimmunoassay for the metabolites of three commonly abused drugs, heroin, cocaine, and cannabinoids. Control stools contained no drug. Meconium from the infants of drug-dependent mothers showed the presence of at least one drug metabolite: 80% of the infants of drug-dependent mothers showed cocaine (range 0.14 to 19.91 micrograms/gm stool), 55% showed morphine (range 0.41 to 14.97 micrograms/gm stool), and 60% showed cannabinoid (range 0.05 to 0.67 micrograms/gm stool). The concentrations of metabolites were highest during the first 2 days; some stools tested positive up to the third day. In contrast, only 37% of the infants had positive results on a urine screen (fluorescent polarization immunoassay method). Paired urine and meconium specimens, both analyzed by radioimmunoassay, showed a higher concentration of drug metabolites in the latter; eight urine samples had no detectable drugs despite a corresponding positive stool test result. We conclude that meconium is useful for drug screening in the neonate.