When [14C] (+/-)-amphetamine sulphate (0.3 mg/kg) was injected into Tamarin monkeys, some 70-80% of the 14C was excreted in the urine in 24 hours. Some 75% of the 24-hour excretion was unchanged drug, 7% was free and conjugated benzoic acid and 7% was hydroxylated in the aromatic ring to give mainly 4-hydroxyamphetamine (Paredrine). With similar doses of [14C] norephedrine hydrochloride nearly 90% of the 14C was excreted in 24 hours, most of this being unchanged drug. Only 3-4% was metabolized at the side chain and there was no aromatic hydroxylation. The results were compared with those obtained earlier in man, rat, rabbit and guinea pig. Quantitatively the metabolites of amphetamine, norephedrine and preludin in the tamarin were more like those in man than in the other three species.