To examine the feasibility of detecting lysergic acid diethylamide (LSD) and its metabolites in hair, LSD was administered to rats with pigmented hair at 0.05, 0.1, 0.5, 1, and 2 mg/kg intraperitoneally once per day for 10 successive days. The rats were shaved just before the first administration, and newly grown hair was collected 4 weeks later. After being washed with 0.1% sodium dodecyl sulfonate and water and being dried in a desiccator, each 20-mg hair sample was extracted with 2 mliter methanol-5N HCl (20:1) under ultrasonication for 1 h and stored at room temperature for 14 h. The extract was evaporated to dryness, extracted from 0.1M NaOH with dichloromethane, and derivatized with a mixture of trimethylsilylimidazole, bis-(trimethylsilyl)acetamide, and trimethylchlorosilane (3:3:2, v/v/v) for gas chromatographic-mass spectrometric (GC-MS) analysis using LSD-d10 or lysergic acid methylpropylamide (LAMPA) as the internal standard. Selected ions were monitored at m/z 395, 293, and 279 for TMS-LSD and at m/z 381, 279, and 254 for the trimethylsilyl derivative of N-demethyl-LSD (TMS-norLSD). LSD and norLSD were also detected by high-performance liquid chromatography (HPLC) with fluorometric detection (excitation, 315 nm; emission, 420 nm). LSD was detected in the rat hair following the lowest dose (0.05 mg/kg), whereas norLSD was only detectable in the hair following the highest dose (2 mg/kg). The same GC-MS and HPLC assays were applied to the analysis of hair from 17 self-reported LSD users, and LSD was detected in two of the samples.