The present work studied the effects of epidermal growth factor (EGF) on the release of thyrotropin (TSH) and prolactin (PRL) from perifused pituitary glands of 200-gram male Wistar rats. Each pituitary gland, cut into halves, was placed in a chamber of a perifusion system connected to a peristaltic pump which conveyed the perifusion medium (Medium 199, pH 7.3, Gibco, USA) from a reservoir to a chamber at a flow rate of 100 µl/min. Each tightly closed chamber contained one pituitary gland and 600 µl medium and it was placed in a water bath at 37 ° C throughout the experiment. One milliliter samples of effluent were collected every 10 min for 60 min to obtain baseline values of TSH and PRL. Thereafter, TSH-releasing hormone (TRH) 10–8M or EGF (10–11, 10–10, 10–9 or 10–8M) were added to individual chambers and the 10-min sampling of effluent continued for 60 min. EGF 10–11M elicited no TSH response, but 10–10 and 10–9M doses induced significant increases in TSH secretion (p < 0.01) with a peak at 10 min after addition of EGF. In another experiment, EGF 10–8M or TRH 10–8M significantly elevated TSH secretion (p < 0.01). However, TRH, but not EGF, stimulated PRL secretion (p < 0.01). In the in vivo studies, the intravenous administration of EGF 10–5 M or TRH 10–5M both induced significant elevation of TSH release at 10 min after the injection (p < 0.02 for EGF and p < 0.01 for TRH). In summary, EGF stimulated TSH secretion from rat pituitary glands in vitro and in vivo, in a magnitude comparable to that