During the last few years, many neuropeptides have been isolated, characterized and synthesized. Neuroendocrinology is one area in which there has been major progress, particularly through the isolation of two new hypothalamic factors, corticotropin releasing factor (CRF) and growth hormone releasing factor (GRF). CRF specifically stimulates pituitary secretion of ACTH and other peptides derived from pro-opiomelanocortin (beta-lipotropin, beta-endorphin), while GRF, together with somatostatin, controls secretion of the growth hormone. Knowledge of the structures of the hypothalamic factors has allowed the synthesis of the native substances as well as many potent analogues with agonist and antagonist properties. These substances have numerous clinical applications. LHRH or its analogues are presently used or being tested in various conditions such as treatment of hormone-related cancers (prostate, breast), endometriosis, idiopathic precocious puberty as well as in sterility problems. The recent availability of long acting somatostatin analogues has raised great therapeutic expectations in various endocrine and digestive diseases. Whereas GRF can be used in the treatment of short stature, CRF has so far not been shown to be a potential important therapeutic agent. However, its clinical application as a diagnostic test is clearly useful in many situations. There is a promising future for the clinical applications of these substances in various endocrine, digestive and perhaps in psychiatric diseases, and in hormone-related cancers.