(-)Deprenyl (selegiline, jumex, eldepryl, movergan) which is closely related to phenylethylamine (PEA) is a drug with a unique pharmacological spectrum. Single dose effects: (a) It is a highly potent and selective inhibitor of B-type monoamine oxidase (MAO). (b) In contrast to other MAO inhibitors it inhibits the noradrenaline releasing effect of tyramine, is therefore free of the 'cheese effect'. Multiple dose effects unrelated to MAO inhibition: (a) It enhances superoxide dismutase and catalase activity in the striatum. (b) It facilitates the activity of the nigrostriatal dopaminergic neurones. (c) It prevents age-related morphological changes in the neurocytes of the substantia nigra. Consequences of multiple dose effects: Compared to salt solution-treated rats, male rats maintained on (-)deprenyl loose their capacity to ejaculate later on; retain for longer their learning ability; and live longer. Freshly diagnosed Parkinson's patients maintained on (-)deprenyl, required levodopa later than their placebo-treated peers. Patients treated with levodopa plus (-)deprenyl live longer than those on levodopa alone. Chronic treatment with (-)deprenyl improves the performance of patients with Alzheimer's disease.