Legal issues are important in drug testing programs, and the most legally defensible drug testing method is to screen urine samples with the enzyme-mediated immunoassay technique (EMIT) and then submit positives from this step to gas chromatography/mass spectrometry (GC/MS). EMIT is comprised of a variety of tests for commonly abused drugs that use specific antibodies to detect the presence of drugs in urine. GC/MS techniques are the most definitive in confirming the presence of drugs in urine. Basic elements needed for an effective and legally defensible drug testing program include a clear and comprehensive policy, secure collection, chain of custody procedures, retained positive samples, an initial screening test, a sophisticated confirmatory test, a medical review officer, retest of retained positive samples in disputed cases, and a quality control system. With the availability of different preparatory procedures for urine samples using GC/MS, the probability that a urine sample will come back falsely positive is virtually nonexistent. Further, studies reveal no situation where both the screening test (immunoassay) and the confirmatory test (GC/MS) cause false positives. Adulterating techniques attempted by inmates and others who want to escape detection of a positive urine sample are described. 32 references and 1 table