The course of plasma β-endorphin/β-lipotropin, cortisol and prolactin (PRL) levels was followed from 0.5 till 5 h after normal delivery in 13 healthy women. Six subjects who did not want to breast-feed their child received 2.5 mg bromocriptine orally 1 h after delivery. After 3 h the effect of the intravenous administration of 200 µg thyrotropin-releasing hormone (TRH) was also measured. Elevated plasma β-endorphin and cortisol levels decreased after delivery in a (log) linear fashion which was not influenced by bromocriptine. TRH elicited a significant short-lived identical increase in plasma β-endorphin/β-lipotropin concentrations in the control and the bromocriptine-treated subjects. TRH similarly delayed the rapid decline in plasma cortisol levels in both groups of women. Basal and TRH-induced PRL levels were rapidly suppressed by bromocriptine. These studies show the presence of a paradoxical increase of β-endorphin/β-lipotropin and cortisol levels in response to TRH occurring shortly after delivery in normal women. This response cannot be mediated by the placenta. The absence of an inhibiting effect of bromocriptine on basal and TRH-induced β-endorphin and cortisol release does not lend support to the hypothesis of the presence of a functionally active intermediate pituitary lobe in man early in puerperium.