A gas chromatography/mass spectrometry (GC/MS) method was developed and validated for the determination of common drugs of abuse in Asia. The method was able to simultaneously quantify amphetamines (amphetamine; AP, methamphetamine; MA, methylenedioxy amphetamine; MDA, methylenedioxymeth mphetamine; MDMA, methylenedioxy ethylamphetamine; MDEA), ketamine (ketamine; K, norketamine; NK), and opiates (morphine; MOR, codeine; COD, 6-acetylmorphine; 6-AM) in human hair. Hair samples (25 mg) were washed, cut, and incubated overnight at 25 degrees C in methanol/trifluoroacetic acid (methanol/TFA). The samples were extracted by solid-phase extraction (SPE), derivatized using heptafluorobutyric acid anhydride (HFBA) at 70 degrees C for 30 min, and the derivatives were analyzed by electron ionization (EI) GC/MS in selected ion monitoring mode. Confirmation was accomplished by comparing retention times and the relative abundances of selected ions with those of standards. Deuterated analogs of the analytes were used as internal standards for quantification. Calibration curves for ten analytes were established in the concentration range 0.1-10 ng/mg with high correlation coefficients (r2 > 0.999). The intra-day and inter-day precisions were within 12.1% and 15.8%, respectively. The intra-day and inter-day accuracies were between -8.7% and 10.7%, and between -5.9% and 13.8%, respectively. The limit of detection (LOD) and limit of quantification (LOQ) obtained were 0.03 and 0.05 ng/mg for AP, MA, MDA, MDMA and MDEA; 0.05 and 0.08 ng/mg for K, NK, MOR and COD; and 0.08 and 0.1 ng/mg for 6-AM. The recoveries were above 88.6% for all the compounds, except K and NK which were in the range of 71.7-72.7%. Eight hair samples from known polydrug abusers were examined by this method. These results show that the method is suitable for broad-spectrum drug testing in a single hair specimen.