The effect of (-) deprenyl was investigated both on the stereotyped behavior and on other types of activities induced by various dopamine (DA) agonists. (-) Deprenyl was given in a single dose, 1 h prior to the DA agonists. 1-2 mg/kg sc (-) deprenyl decreased the stereotypy induced by amphetamine (AMPH, 2.5 mg/kg sc), but 20 mg/kg was needed to reduce the stereotypy-inducing effect of apomorphine (APO, 0.3 mg/kg sc). The stereotypy-inducing effect of phenyl-ethyl-amine (PEA, 40 mg/kg sc) was significantly enhanced by 0.25 mg/kg sc (-) deprenyl pretreatment. The PEA or AMPH-induced increase in the horizontal activity (locomotion) and the vertical activity (rearing) remained unchanged after a single dose of (-) deprenyl, showing that this drug acts primarily on the nigro-striatal dopaminergic system.