An instrumental high-performance thin-layer chromatographic (HPTLC) technique for the determination of lysergic acid diethylamide (LSD) in urine was developed. Before chromatographic separation, a single-step extraction with alkaline wash is performed. The procedure can detect less than 1 microgram LSD/L urine. Results of HPTLC determination are compared with those from a radioimmunoassay (RIA) procedure.