Résumé : Five normal men were injected intraSummary venously 200 μg. of synthetic thyrotrophin-releasing hormone (T.R.H.). Blood was collected every 5 or 10 minutes and assayed for thyroid-stimulating hormone (T.S.H.), human growth hormone, luteinising hormone, hydrocortisone, and pituitary prolactin. T.S.H. levels reached peak values 20 to 40 minutes after the injection. Hydrocortisone, H.G.H., and L.H. did not exhibit any systematic variation. The T.R.H. injection was followed within 5 minutes by a release of prolactin, with a peak value at 10 minutes. These data indicate a lack of specificity of T.R.H. and suggest that in man it acts as a prolactin-releasing factor. Intravenous T.R.H. administration should become a very useful clinical test for the investigation of the hypothalamo-pituitary relationships, with special respect to prolactin secretion. © 1972.