Two types of dopamine receptor whose stimulation affects cellular cyclic AMP have now been identified. In tissues as different as insect ganglia and mammalian neostriatum, stimulation of the dopamine receptor called D-1 increases formation of cyclic AMP(1-6), whereas stimulation of the second type of dopamine receptor (D-2)(7-11), first identified in the rat pituitary gland, reduces cyclic AMP formation. Recently, a receptor with the pharmacological properties of the D-2 receptor has also been found(12-14) in the rat neostriatum; we show here that stimulation of this receptor is followed by a reduction in cyclic AMP formation induced by V stimulation with D-1 agonists.