Chicken anterior pituitary glands were incubated in vitro with different doses of synthetic thyrotrophin releasing factor (TRF). The release of both thyroid stimulating hormone (TSH) and luteinizing hormone (LH) was then monitored. Relatively low doses of TRF (2 and 4 ng/ml) significantly increased the re-lease of TSH, whereas at a lower dose (1 ng/ml) and at a higher dose (20 ng/ml) no stimulation was observed. The secretion of LH remained unchanged by any TRF treatment. An acid extract of chicken hypothalami significantly increased the secretion of both LH and TSH from the bird pituitary tissue.