Abstract: We have studied the metabolism of phenmetrazine, phendimetrazine and morazone, and their metabolites in urine. A sensitive, specific method using GC / NPD was applied to the determination of the rate of excretion of the drugs quantitatively, diphenylamina being used as the internal standard. The ether extract was derivatized with TFAA reagent, the metabolites and their TFA derivatives were identified by GC / NPD and GC/MSD methods. Norephedrine, cathine, ephedrine and pseudoephedrine in small amount were identified.