In 1993, NIJ funded a project designed to replicate the findings of an earlier study that had examined drug use among juvenile offenders using self reports, urinalysis, and hair assays. The original study showed that hair analysis revealed seven times as much cocaine use as was detected by urinalysis. Hair entraps drugs or their metabolites for much longer periods than urine and represents an alternative medium for estimating the use of rapidly excreted drugs. Hair Assays and Urinalysis Results For Juvenile Drug Offenders reports the findings from the replicated study which confirmed those made earlier, although only a fourfold difference was found between hair and urine assay results for cocaine. The study also identified sample members at risk for substance abuse independently from the bioassay or self report.