Opiates and stimulants are typically detectable in plasma or saliva for up to 12 hours after injection but may be detected in urine for several days. At the same time, they are embedded in hair as it is formed and first appear some days after ingestion. The drug or metabolite appears to remain for the lifetime of the hair after it is formed; therefore, hair can be examined in segments to detect drug use over a much longer period of time. For hair drug analysis, the most sensitive and widely used techniques are radioimmunoassay and gas chromatography. Quality control issues in hair drug analysis are discussed, public support for drug testing in certain occupations is considered, and the ease of conducting hair drug analysis is noted. Future technological developments in drug testing that involve hair analysis are considered. 20 references