[3H]-dopamine (DA) binding to bovine anterior pituitary membranes was measured using sensitive in vitro ultrafiltration and centrifugation techniques. The specific interaction of [3H]-DA with the membrane fraction reached a steady-state level within 15 min at 30°C and was reversible by incubating with excess nonradioactive DA. Scatchard analysis suggests the presence of 2 sites for DA specific binding having K < j values of 4.4 × 10–10 M and 4.7 × 10–8 M, respectively. Correspondingly, the total receptor concentrations were calculated to be 336 and 2,340 pmoles/g protein. Blockade of [3H]-DA binding was produced most effectively by ergocryptine and apomorphine. Perphenazine and haloperidol were considerably less active and pimozide did not compete. The importance of DA in the regulation of prolactin (Prl) secretion and the characterization of pituitary DA receptor sites are dis