A procedure is presented for the detection in human hair of forensically relevant benzodiazepines, i.e. nordiazepam, oxazepam, bromazepam, diazepam, lorazepam, flunitrazepam, alprazolam and triazolam. The method involves decontamination of hair with methylene chloride, pulverization in a ball mill, incubation of 50 mg powdered hair in Soerensen buffer (pH 7.6) in the presence of prazepam-d5 used as internal standard, liquid-liquid extraction with diethyl ether-chloroform (80:20, v/v) and gas chromatography-mass spectrometry using negative chemical ionization after derivatization with N,O-bis(trimethylsilyl)trifluoroacetamide plus 1% trimethylchlorosilane. The limits of detection for all benzodiazepines ranged from 1 to 20 pg/mg using a 50-mg hair sample. Coefficients of variation and extraction recoveries, ranging from 7.4 to 25.4% and 47.6 to 90%, respectively, were found suitable for a screening procedure. One hundred and fifteen samples were submitted to this screening procedure, and specimens tested positive for nordiazepam (0.20-18.87 ng/mg, n=42) and its major metabolite oxazepam (0.10-0.50 ng/mg, n=14), flunitrazepam (19-148 pg/mg, n=31), lorazepam (31-49 pg/mg, n=4) and alprazolam (0.3-1.24 ng/mg, n=2). Bromazepam, diazepam and triazolam were not detected.