Abstract: Cyclic analogues of the tridecapeptide hormone, .alpha.-melanotropin. (.alpha.-melanocyte stimulating hormone, .alpha.-MSH), wherein a physiologically stable intramolecular interaction exists (1) between the amino acid residue at position 4 and an amino acid residue at position 10 or 11, and/or (2) between the amino acid residue at position 5 and an amino acid residue at position 10 or 11. Preferred analogues, e.g., [half-Cys.sup.4, half-Cys.sup.10 ]-.alpha.-MSH display greatly increased in vitro potency, prolongation, and resistance to enzymatic degradation.

Abstract: Analogues of the tridecapeptide hormone, .alpha.-melanotropin (a-melanocyte stimulating hormone, .alpha.-MSH) of the formula:Ac-Ser.sup.1 -Tyr.sup.2 -Ser.sup.3 -Y.sup.4 -Glu.sup.5 -His.sup.6 -X.sup.7 -Arg.sup.8 -Trp.sup.9 -Gly.sup.10 -Lys.sup.11 -Pro.sup.12 -Val.sup.13 -NH.sub.2wherein X and Y are amino acid residues and X is in a D-isomeric configuration. Preferred analogues, e.g. [Nle.sup.4, D-Phe.sup.7 ]-.alpha.-MSH, display increased in vitro and in vivo potency, prolongation and serum stability characteristics and may be covalently bonded to other elements or compounds (e.g., radioisotopes of iodine) without significant loss of biological activity.

Abstract: Effects of endogenous glucagon in mammals are diminished by administration of compositions including certain semi-synthetic analogs of glucagon. Preferred analogs include [N.sup..alpha. -TNB, HArg.sup.12 ]glucagon and [dHis.sup.1 ][N.sup..alpha. -TNB, HArg.sup.12 ]glucagon, parenterally administered at doses of from about 0.05 to about 50 mg of analog per kg of body weight.