Given the limitations of self-reports on drug use, testing for drugs of abuse is important for most clinical and forensic toxicological situations, both for assessing the reality of the intoxication and for evaluation of the level of drug impairment. It is generally accepted that chemical testing of biological fluids is the most objective means of diagnosis of drug use. The presence of a drug analyte in a biological specimen can be used to document exposure. The standard in drug testing is the immunoassay screen, followed by the gas chromatographic-mass spectrometric confirmation conducted on a urine sample. In recent years, remarkable advances in sensitive analytical techniques have enabled the analysis of drugs in unconventional biological specimens such as hair. The advantages of this sample over traditional media, like urine and blood, are obvious: collection is noninvasive, relatively easy to perform, and in forensic situations it may be achieved under close supervision of law enforcement officers to prevent adulteration or substitution. The window of drug detection is dramatically extended to weeks, months or even years when testing hair. It seems that the value of alternative specimen analysis for the identification of drug users is steadily gaining recognition. This can be seen from its growing use in preemployment screening, in forensic sciences, in clinical applications and for doping control. Hair analysis may be a useful adjunct to conventional drug testing in urine. Methods for evading urinalysis do not affect hair analysis. The aim of this review is to document toxicological applications of hair analysis in drug detection.