The incidence of drug use is discussed; major classes of drugs of abuse and their effects are delineated, including heroin and the opiates, cocaine and crack, marijuana, the hallucinogens, sedatives, and amphetamines. Techniques for testing urine samples for drugs are described -- enzyme immunoassay, radioimmunoassay, thin-layer chromatography, and gas chromatography/mass spectrometry. The reliability of these tests and the problem of false positives are considered. Drug-testing policies and practices are described, and case law regarding testing is reviewed with attention to such legal issues as the right to privacy, and reasonable suspicion and probable cause. Photographs, glossary, 16 notes, index, and 64 references.