Several polypeptide analogs of the known members of the corticotropin releasing factor (CRF) family have been synthesized and tested including human and rat CRF which have the formula: H-Ser-Glu-Glu-Pro-Pro-Ile-Ser-Leu-Asp-Leu-Thr-Phe-His-Leu-Leu-Arg-Glu-Val-Leu-Glu-Met-Ala-Arg-Ala-Glu-Gln-Leu-Ala-Gln-Gln-Ala-His-Ser-Asn-Arg-Lys-Leu-Met-Glu-Ile-Ile-NH.sub.2. Peptides are herein disclosed that are potent competitive antagonists of CRF in mammals. One which has been found to be particularly potent is: H-Leu-Asp-Leu-Thr-Phe-His-Leu-Leu-Arg-Glu-Met-Leu-Glu-Met-Ala-Lys-Ala-Glu-Gln-Glu-Ala-Glu-Gln-Ala-Ala-Leu-Asn-Arg-Leu-Leu-Leu-Glu-Glu-Ala-NH.sub.2. These antagonists or pharmaceutically or veterinarily acceptable salts thereof, dispersed in a pharmaceutically or veterinarily acceptable liquid or solid carrier, can be administered to mammals, including humans, to achieve a prevent elevation of ACTH, .beta.-endorphin, .beta.-lipotropin, other products of the pro-opiomelanocortin gene and corticosterone levels and/or a lowering of brain-mediated responses to stress over an extended period of time. They may also be used to affect mood, memory and learning, as well as diagnostically.