Hair testing in the workplace for drugs of abuse such as cocaine, opiates, methamphetamine, marijuana, and PCP, has many safeguards and advantages over other forms of drug testing. The advantages of hair analysis testing for employers include: (1) hair testing provides a wide window of detection of drug use, typically 3 months; (2) the hair matrix provides a highly protective and inert environment for analytes; (3) sample tampering procedures effective against urinalysis such as adulteration of the specimen cannot be employed against hair testing; and (4) normal care of hair, including bleaching, are ineffective evasive tactics if appropriate extraction procedures involving the inaccessible domain of hair are used. The advantages of testing for employees include: (1) the ability to obtain a second sample provides important protection against errors at the collection site; (2) hair is conveniently collected without embarrassment under close observation; and (3) employees can demonstrate by hair analysis that they have overcome their drug problems. The relative clinical sensitivities of hair and urine tests show that even the most challenging hair assay, marijuana, is as effective at detecting drug users as the best urine test, even when urinalysis is used under conditions where evasive tactics can not be applied. The safety and effectiveness of hair testing depends on the use of highly effective wash and extraction procedures and on the confirmation of all positive screening test results. Hair testing is not affected by the “poppy seed” problem; provides an approximate measure of the severity of an individual’s drug use; cannot be thwarted by cutting head hair off (can use body hair or fingernail analysis); and isn’t biased by hair color. 8 figures, 15 tables, 39 references