The enzyme systems and the mechanisms involved in the biotransformation of amphetamine, methamphetamine and the related compounds are briefly reviewed. The major themes discussed in this review are : 1) cytochrome P-450 isozymes involved in the deamination, N-dealkylation and aromatic hydroxylation ; 2) the role of cytochrome P-450 and flavin-containing monooxygenase in the N-dealkylation ; 3) the enzymes functioning as hydroxylamine reductase and oxidase ; 4) molecular mechanisms of deamination and N-dealkylation ; 5) metabolic-intermediate complex.