Octopamine (50-250 microgram ivc) activates both noradrenergic and dopaminergic system of the rat. In rats pretreated with reserpine or reserpine and FLA-63 the stimulatory action of octopamine was not inhibited, but even enhanced. Only selective destruction of dopamine containing neurons (6-hydroxydopamine, 200 microgram ivc, given 1 hr after desipramine, 25 mg/kg ip) prevents octopamine-induced hyperactivity. Octopamine depressed the noradrenaline level in the rat brain and increased utilization of the amine, but did not affect the level and utilization of dopamine.