An injection of 250 micrograms 6-OHDA into the right cerebral ventricle of adult rats tested after 45 days led to a reduction of the run performance on the treadmill compared with the control group, but only in the first period of this test, repeated 10-11 times, every 2-3 days. This behavior was more obvious in male and in exercise-enduring rats. The histological examination proved partial destruction of central monoaminergic (especially dopaminergic) structures in the 6-OHDA treated rats. 24-48 hours after peripheral injections of 6-OHDA (100 mg/kg b. w.) a considerable reduction of the run and swim performance (acute exercise till exhaustion) occurred. Falck's histofluorescence method proved large destructions of the noradrenergic innervation in the iris; 6-OHDA injected i.p. into neonatal rats had similar effects.