The selectivities of various dopamine agonists and antagonists for dopamine D1 and D2 receptors were obtained by comparing their relative dissociation constants for inhibiting the binding of [3H]SCH 23390 at D1 receptors (calf caudate nucleus) and at D2 receptors (pig anterior pituitary tissue). The most selective agonists were SK&F 38393 (for D1) and (+)-PHNO (for D2), while the most selective antagonists were SCH 23390 (for D1) and raclopride or eticlopride (for D2).