Many widely used methods for derivatizing drugs of the amphetamine group for GC/MS are problematic. The difficulties with these methods include incompatibility with other derivatizing agents, short column life, lack of abundant high molecular weight ions, and the potential for interference from other drugs. The present procedure is an effort to reduce some of these problems by the use of a novel derivatizing agent, N-methyl-N-t-butyldimethylsilyl trifluoroacetamide (MTBSTFA). We describe here an MTBSTFA derivatization method for amphetamine (AMP) and methamphetamine (MAMP) that leads to stable derivatives that are well-separated from potential interferences and features high molecular weight fragments suitable for selected ion monitoring. The procedure is linear to approximately 3000 ng/mL for both AMP and MAMP and appears to be both precise and sensitive. Furthermore, it seems to have no adverse effect on column life.