Many laboratories use an enzyme immunoassay procedure called EMIT (enzyme multiplied immunoassay technique) to screen urine samples for 9-carboxy-THC and other marijuana metabolites. The cannabinoid EMIT test involves a drug-specific antibody that binds to 9-carboxy-THC and other cannabinoid metabolites. The EMIT test system can be used to determine the approximate cannabinoid co ncentrtion in a urine specimen. Although the accuracy of the EMIT test has been documented extensively, its manufacturer recommends that EMIT-positive results be confirmed in certain types of urinanalysis testing programs. One confirmation procedure for marijuana use is high performance thin-layer chromatography, which can identify 9-carboxy-THC, the primary metabolite of THC in human beings. Instrument errors or handling and clerical mistakes are remaining sources for false positives. These can be eliminated by the careful observance of written procedures. By using the EMIT 100 ng/ml cutoff, the smoking of a single high-quality marijuana cigarette can be detected for at least 2 and possibly up to 7 days after use. Frequent use may be detected for up to 3 to 4 weeks. Urinalysis can detect prior drug use but cannot be used to evaluate or prove the drug's impairment effect.