The study demonstrates that, in May 1987, testing urine for drugs of abuse can be accurate. All laboratories challenged in this study currently perform such testing under contract and are involved in monthly proficiency testing and in-service training (AACC's Surveys Plus and In-Service Training Program in Toxicology). The laboratories were challenged to detect drugs at the concentrations at which they accept business. We suspect that when results of studies of this kind have been reported previously, the laboratories may have been scored inaccurately because they used technology designed to detect higher concentrations of the drugs than were weighed into the study specimens. This points up the need for laboratories and clients to be specific about the threshold concentrations used to report positives and policies for reporting positives detected below those concentrations.