The cardiovascular effects of single intravenous injections of dopamine (DPA; 2, 5, 10 and 25 micrograms/kg) were evaluated in swine, less than or equal to 1 day to 2 months of age, anesthetized with halothane in 50% N2O-O2. Mean aortic pressure increased following all doses of DPA in swine less than or equal to 1 month of age. Renal vasoconstriction was obtained with 5-25 micrograms/kg in the younger animals and with 25 micrograms/kg in the oldest. After 2 micrograms/kg, renal vasodilation occurred in 2-month-old swine. Femoral and carotid vasoconstriction was elicited in day-old swine after 5-25 micrograms/kg DPA, but carotid vasodilation occurred in the oldest swine. Responses to 25 micrograms/kg DPA after combined alpha and beta adrenergic receptor blockade were generally vasodilator. Thus, dopaminergic receptors were unmasked and a postnatal maturation of these receptors was revealed.