Metoclopramide (MET), a potent dopamine receptor-blocking drug, or saline was administered to 125 term pregnant women at various time intervals (5-412 min) before delivery. Maternal serum was obtained before and after MET injection. Cord blood was obtained at delivery in MET-treated and saline-treated (control group) women. No significant changes in serum TSH, T4, T3, or rT3 concentrations were observed in maternal or cord blood after MET administration. These results suggest that, in contrast to euthyroid nonpregnant women and men, MET administration does not induce a rise in serum TSH concentration in term pregnant women or in the term fetus. Thus, the dopaminergic inhibitory effect on anterior pituitary TSH secretion may not be an important factor in TSH regulation during pregnancy or in the fetus, or the dose of MET employed may be unable to overcome the dopamine inhibitory effect.