A traffic accident caused by a man who declared that he was driving under influence of drugs (Temesta), led our laboratory to develop a procedure for the detection and the quantification of lorazepam in human hair. The method involves decontamination of hair with dichloromethane, incubation in Soerensen buffer (pH 7.6) in the presence of lorazepam-d4, liquid-liquid extraction with diethylether-chloroform (80:20, v/v) at pH 8.4, derivatization by silylation and detection by GC-MS/NCI. The increasing concentrations of lorazepam from the end to the roots of a 16-cm-long hair strand (i.e. 31 pg/mg, 40 pg/mg and 49 pg/mg) proved that the driver had taken the drug over a long period of time.