Hair analysis and urinalysis are complementary tests for establishing drug use. Hair analysis provides long-term information, from months to years, concerning both the severity and pattern of drug use. In contrast to this, urinalysis can indicate only drug use, and then generally only that which has occurred within the last 2-3 days. Field studies have demonstrated that hair analysis is considerably more effective than urinalysis at identifying drug users. This difference is due to the wider surveillance window of hair analysis and to the susceptibility of urinalysis to evasive maneuvers. The main concerns with urinalysis are endogenous evidentiary false positives caused by passive drug exposure, e.g., ingestion of poppy seed. This problem arises from the hypersensitivity of the urine test, i.e. the need to use low cut-off levels in order to compensate for the temporary recording of drug use. This problem does not occur with hair analysis since its wide window of detection and permanent record of drug use ensure that the detection efficiency of the test is not compromised by the use of more effective cut-off levels guarding against passive endogenous drug exposure. On the other hand, exogenous evidentiary false positives due to external contamination of hair by drugs present in the environment (e.g., smoke) are the main concern of hair analysis. This problem, however, can be effectively avoided by washing the hair specimen, by kinetic analyses of the wash data, and by measurement of metabolites. The possibility of bias due to race and/or hair color is avoided by the exclusion of melanin from the analysis of hair. The safety and effectiveness of hair testing has been established by extensive field studies with over 400,000 specimens.