It has long been considered that one of the drawbacks to the routine clinical use of the hypothalamic releasing factors for diagnostic or therapeutic purposes (when they would become available) would be that they could not be administered per os, being polypeptides – which usually are susceptible to proteolytic enzymes to be found in the gastrointestinal tract. The observation that the half life of the hypothalamic releasing factors is of only a few minutes, a fact probably related to the existence of enzymatic plasma inactivation, indeed demonstrated in the case of hypothalamic TRF (1,2,3,4) is another somewhat unfortunate circumstance when considering the possible clinical application and uses of these substances. Furthermore, it has long been recognized that availability of synthetic products would be a requisite for any clinical studies and/or use in view of the extremely small quantities of the natural substances of hypothalamic origin available from extraction methods.