The presence of opiates and benzoylecgonine, the major metabolite of cocaine, in the urine was detected by means of enzyme immunoassay in a series of 120 smugglers who had either ingested or inserted into their rectum cocaine or heroin packaged for transportation. There was a striking relation between the presence of drugs in the urine and swallowing of drug-filled bundles (cocaine 49 of 50 cases, heroin 9 of 10). The proportion of positive results was also high in cases of rectal insertion (cocaine 2 of 2, heroin 35 of 58). In 30 cases of cocaine-packet ingestion, serial measurements showed that the accuracy of the test progressively decreased with respect to the detection of residual packets in the body. Drug detection in the urine of suspected body-packers seems to be a useful test, positive results justifying subsequent radiological investigations.