Hair analysis as a means of drug testing is based on the hypothesis and subsequent documentation that the blood circulation to hair roots results in the incorporation into the hair strand or follicle of drugs that circulate in the blood. After the hair is washed and cut into segments that relate to a specific time period, the hair is dissolved through a series of steps. This allows for the release of proteins related to the drugs used, proteins that can then be identified by specific antibodies. In this way, the samples can be scanned for the presence (and perhaps amount) of heroin, methadone, phencyclidine, cocaine, marijuana, nicotine, and the benzodiazepines. This technique for drug testing has promising potential for determining the presence or absence of drug taking, although its validity regarding the quantity of the substance ingested is questionable. Analysis of hair samples is thus a potentially important complement to urine testing, with the former of greatest use for assessments over time and the latter more important regarding recent ingestion. The technique should be re-evaluated once a wider range of research groups have determined the validity of the methods and when, and if, more laboratories have used this procedure.