A GC-MS method has been developed for the detection of amphetamine, methamphetamine, and the ephedrines, in seizures and the urine, based on on-GC condensation (derivatization) with cyclohexanone. The method is simple: the dried seizure material or the urine extract was mixed with cyclohexanone and injected into the GC-MS. The method was found to be superior to the methods based on acyl and trimethylsilyl (TMS) derivatization. Unlike for the acyl and TMS derivatives, the molecular and fragment ions of the cyclohexanone condensation products (cyclohexanone derivatives) were of substantial abundance, a useful property in unambiguous compound characterization. Furthermore, the high stability of the "derivatizing" reagent, cyclohexanone, compared with acyl and TMS derivatizing reagents, is a useful property in method development. The present method has proved selective and, tentatively, sensitive enough in the following areas (where methods based on acyl and TMS derivatization, as tested in this laboratory, have failed): (a) detection of amphetamine as a metabolite of methamphetamine; (b) detection of norpseudoephedrine as a metabolite of pseudoephedrine; (c) detection of amphetamine as an impurity of methamphetamine; (d) detection of cathine (norephedrine) as a constituent of Khat leaves; and (e) differentiation of Khat use from phenylpropanolamine use.