The findings suggest that hair analysis for 6-acetylmorphine can be used to distinguish between heroin use and other types of opiate exposure. These findings are significant because the short half-lives of both heroin and 6-acetylmorphine make it difficult to detect them in blood, plasma, or urine samples. The discovery that heroin and its metabolite remain in hair over extended periods of time reflects the unusual stability of heroin analytes in a protein matrix. However, environmental contamination can potentially produce false positives during opiate testing; the results suggest that environmental contamination will be difficult to differentiate from active heroin use. Nonetheless, this procedure could be used to supplement urine testing when only morphine is detected. 2 figures, 2 tables, and 26 references