A sensitive method for the simultaneous analysis of cocaine, benzoylecgonine (BE), and ecgonine methyl ester (EME) in human hair by gas chromatography/chemical ionization mass spectroscopy (GC/CIMS) is described. Hair samples are cut into 1-cm sections, washed with 1% sodium dodecylsulfate, rinsed with deionized water and methanol, and then digested overnight in a solution containing Tris buffer, sodium dodecylsulfate, Proteinase K, and dithiothreitol. Digested hair samples are extracted with Bond Elut Certify™ solid-phase extraction columns, derivatized with N-methyl-N-(tertbutyldimethylsilyl)-trifluoroacetamide (MTBSTFA), and analyzed by GC/CIMS using isobutane as reagent gas. This method is quantitative, does not cause degradation of cocaine, and requires as little as 5 mg of hair. Analysis is performed on a Finnigan ITS-40 ion trap mass spectrometer interfaced with a Varian 3400 gas chromatograph equipped with a Model 1075 split/splitless injector and a J&W DB-5 capillary column. Full scan spectra are used for identification of cocaine and its metabolites. Quantitation is based on peak area ratios of the MH+ ions, as follows: 304 for cocaine, 404 for BE-TBDMS, 314 for EME-TBDMS, and 340 for the internal standard, difluorococaine. This method can be used to quantitate cocaine at concentrations of 0.1 to 100 ng/mg hair. The coefficients of variation (%CV) at a drug concentration of 1 ng/mg hair are 10.3, 16.3, and 27.7% for cocaine, BE, and EME, respectively.