The purpose of this randomized, double-blind clinical study was to evaluate the efficacy of the antidopaminergic agent metoclopramide (MC) in the treatment of puerperal lactational insufficiency, and prolactin, TSH and free thyroxine responses of the mother and the child to this therapy. Therefore, 11 women received MC (10 mg 3 times daily orally) and 14 a placebo for 3 wk. MC increased the serum concentration of PRL from 57.5 + 45.5 U/l to 315.0 + 300.0 U/l (P less than 0.001), and the amount of daily milk yield in 8 women with established lactational deficiency rose from 285 + 75 ml to 530 + 162 ml (P less than 0.01) while the placebo was ineffective. Serum concentrations of TSH and free thyroxine did not change during either of the treatments. Serum concentrations of PRL, TSH and free thyroxine in the infants were similar in both groups and remained unchanged throughout the study. Our results suggest that MC is useful in the treatment of deficient puerperal lactation, and it does not stimulate the pituitary lactotropes or thyrotropes of the nursing infants.