From a population of 850 boys in the first grade at public schools, 503 were selected on the basis of a risk scale for antisocial behavior. All of the 850 boys who scored in the upper 30th percentile of the distribution on a self-reported antisocial behavior scale were matched with an equal number drawn by lot from the lower 70 percent of the distribution. From this sample, 301 students accepted the invitation to participate. A subject's exposure to lead was measured by K x-ray fluorescence spectroscopy of the tibia when the subject was 12 years old. Outcome measures were the Child Behavior Checklist (CBCL), teachers' and parents' reports, and subjects' self-report of antisocial behavior and delinquency at 7 and 11 years old. Subjects, teachers, and parents were "blind" to the bone lead measurements. At 11 years old, parents reported a significant lead-related association with the following CBCL cluster scores: somatic complaints and delinquent, aggressive, internalizing, and externalizing behavior. Teachers reported significant associations of lead with somatic complaints; anxious/depressed behavior; social problems; attention problems; and delinquent, aggressive, internalizing, and externalizing behavior. High-lead subjects reported higher scores on subjects' self-reports of delinquency at 11 years old. The study concludes that lead exposure is associated with increased risk for antisocial and delinquent behavior, and the effect follows a developmental course. 7 tables, 3 figures, and 36 references