The effect of bradykinin (BK) on the release of β-endorphin-like immunoreactivity (β-EpLI) in rats was studied in vivo and in vitro. Intraperitoneal injection of BK at 5 µg/100g body weight resulted in significant increase in the plasma β-EpLI level after 15 min. BK at concentrations of 10–12–10–7M also caused dose-dependent stimulation of β-EpLI release from dispersed cells of rat anterior pituitary. On gel chromatography, the β-EpLI released by incubation of the cells with 10–7M BK separated into two components, eluted in the same positions as human β-lipotropin and human β-endorphin, respectively. BK did not stimulate β-EpLI release in Ca++-free medium. Addition of 10–3 M verapamil or 10–6M dexamethasone to the incubation medium inhibited BK-induced β-EpLI release from the cells. Quabain (10–5M) also stimulated β-EpLI release, but its effect was not additive with that of BK. These results indicate that BK stimulates β-EpLI release and that calcium ion is involved in the