The effect of intracerebral administraton of antagonists of dopamine and noradrenaline upon the locomotor stimulation induced by intraperitoneal injection of d-amphetamine sulfate in rats was investigated. Inj ection of low doses of the dopamine antagonist haloperidol (2.5 mug and 5 mug) bilaterally into the nucleus accumbens antagonized the locomotor stimulation following d-amphetamine. No significant inhibition was observed following administration of the alpha-adrenergic antagonist phentolamine or thhe beta-adrenergic antagonist propranolol into the nucleus accumbens. Injection of the dame doses of haloperidol into the caudate nucleus did not inhibit the d-amphetamine induced locomotor activity in contrast to the effects seen following injection into the nucleus accumbens. The results confirm the significance of dopaminergic mechanisms for the locomotor stimulant effect of d-amphetamine and indicate that the mesolimbic dopamine system plays an important role in this respect.