Abstract: This paper presents a method to detect the main metabolites of heroin: 6-monoacetylmorphine (6-MAM) and morphine (MOR) in human hair using GC/MS-SIM. The hair specimens were washed with special solvents and cut into about 0.5 mm pieces. Ethylmorphine was added as internal standard and HCl solution for hydrolysis. After hydrolysis, 6-MAM and MOR were extracted by a mixture of solvents (chloroform—isopropyl alcohol—heptane 50∶17∶33). The residue of the extract was derivatized with N-methyl-N-trimethylsilyl trifluoroacetamide(MSTFA), then the trimethylsilyl(TMS)derivatives were qualitatively and quantitatively analyzed using GC/MS-SIM. The correlation coefficients for 6-MAM and MOR were 0.9996 and 0.9997, respectively. The recoveries of both 6-MAM and MOR were over 50%. The RSD of withinday and between-day was less than 8% and 10%, respectively. The lower limit of detection of both 6-MAM and MOR was 0.5 ng·mg^-1. Hair samples of 12 drug abusers were analyzed using this method, 8 of them gave positive results. This method is simple, accurate and sensitive. It is very suitable for routine case work.