(-)Deprenyl (Selegiline), the N-propargyl analogue of (-)methamphetamine, is the only drug in clinical case which, by enhancing the impulse propagation mediated release of noradrenaline and dopamine in the brain (catecholaminergic activity enhancer, CAE, effect), keeps in small doses without side-effects the catecholaminergic brain system on a higher activity level. (-)Deprenyl stimulates the catecholaminergic neurons selectively in the brain because, in contrast to PEA and the amphetamines which induce the continuous release of noradrenaline and dopamine from their intraneuronal stores, (-)deprenyl is devoid of this property. It is due to the CAE effect that a) the maintenance of rats on (-)deprenyl during the postdevelopmental phase of their life slows the age-related decline of sexual and learning performances and prolongs life significantly; b) patients with early, untreated Parkinson's disease maintained on (-)deprenyl need levodopa significantly later than their placebo-treated peers, and when on levodopa plus (-)deprenyl, they live significantly longer than patients on levodopa alone; and c) in patients with moderately severe impairment from Alzheimer's disease, treatment with (-)deprenyl slows the progression of the disease. It is reasonable to expect that a prophylactic low dose administration of a safe catecholaminergic activity enhancer substance during the postdevelopmental phase of life will slow the age-related decline of behavioral performances, delay natural death and decrease susceptibility to Parkinson's disease and Alzheimer's disease.