Twenty hair samples obtained from Bolivian mine workers who chewed 3-8 g of coca leaves daily for several years were analyzed for cocaine and its main metabolites, benzoylecgonine (BZE) and ecgonine methyl ester (EME). A new method was developed for the detection and quantitation of cocaine and its metabolites, BZE and EME, from hair in a single procedure. The hair samples were washed, cut into 56 segments (2-cm length), pulverized, and incubated with phosphate buffer and the enzyme beta-glucuronidase-arylsulfatase. After solid phase extraction and derivatization with pentafluoropropionic anhydride/pentafluoropropanol, the drugs were identified and measured by gas chromatography/mass spectrometry (GC/MS) using deuterated cocaine, BZE, and EME as internal standards. The method is reproducible (cocaine, CV = 8%; BZE, CV = 14%) and the detection limit for cocaine and BZE was 0.1 ng/mg, for EME 1 ng/mg. In the different hair segments, cocaine was found to be present in concentrations between 1.4 to 50.6 ng/mg, benzoylecgonine from 0.4 to 17.6 ng/mg, and ecgonine methyl ester traces below the calibration curve of approximately 12.9 ng/mg. In 95% of the cases cocaine exceeded BZE and EME in concentration.