Abstract: In a phosphate buffer of pH 9,opiates (i.e.,morphine,6-monoacetylmorphine and codeine) in human blood sample were extracted ultrasonically with a mixture of chloroform,iso-propanol and n-heptane(50+17+33 by volume) at 30 ℃ for 10 min. After centrifugation,the supernatant liquid was taken and evaporated to dryness by blowing at room temperature. The residue was dissolved with acetylacetate and derivatized with the reagent MBTFA. An aliquot of 1 μL of the derivitized solution was taken for GC-MS determination. Values of DL (3S/N) found for the 3 opiates mentioned above were 1,2 and 3 μg·L-1 respectively. Ethyl morphine was used as internal standard. Ranges of linearity of calibration curves for the 3 opiates were same,in the range of 10-1 000 μg·L-1. Recovery and precision of the method were tested by addition of the opiate standards at 3 different concentration levels,giving values of recovery in the ranges of 82.4%-85.5% (for morphine),95.7%-99.1% (for 6-monoacetylmorphine) and 97.5%-101.2% (for codeine);and values of RSD′s (n=5) in the ranges of 4.1%-11.2% (within day) and 4.9%-12.1% (inter day).