Dopamine is frequently used in neonatal intensive care for its vasopressor, renal vasodilating, and cardiac inotropic properties. The effect of i.v. dopamine infusion on neonatal pituitary hormone secretion is currently unknown. We observed strikingly low serum concentrations of growth hormone (GH) and prolactin (PRL) during a therapeutic, standardized, isovolumetric, partial exchange transfusion (blood sampling every 20 min for 6 h) in two polycythemic neonates requiring intensive therapy, including continuous dopamine infusion. In addition, the secretion of GH and PRL was studied in three neonates with symptomatic polycythemia (gestational age 34-38 wk; birth weight 2110-2530 g; postnatal age 10-30 h) during a partial exchange transfusion, including an intervening dopamine infusion (8 micrograms/kg/min i.v. for 2 h). The GH and PRL profiles were evaluated by deconvolution analysis. Initially, the three newborns exhibited high-amplitude, pulsatile GH secretion and continuously elevated PRL release. During the dopamine infusion, GH secretion was virtually abolished and PRL release was reduced by at least 50%. Dopamine withdrawal was associated with a rebound release of GH and PRL. Finally, serum GH and PRL concentrations were studied in nine nonpolycythemic newborns (gestational age 31-40 wk; birth weight 1680-4000 g; postnatal age 2-28 d) at the end of a prolonged dopamine infusion (3-5 micrograms/kg/min i.v. for 2-27 d). Within 2 h after dopamine withdrawal, GH and PRL levels increased a median 3-fold and 10-fold respectively. These data concord to indicate that dopamine is a potent inhibitor of GH and PRL secretion in the human newborn.