Abstract: The method for the analysis of hydrocodone and its metabolite in urine by GC/MSD is reported. The urine was hydrolysed with HCl and extracted with diethyl ether/isopropanol. The gas chromatography/mass spectrometric properties of trimethylsilyl ether of hydrocodone, first reacted with methoxyamine to protect the carbonyl group, were studied. This method is sensitive and rapid for the determination of hydrocodone, codeine and dihydrocodeine.