New cyclo:peptide(s) are atrial natriuretic factor agonists - useful as hypotensives, vasodilators, spasmolytics and broncholytics, as ligands in receptor binding assays and for purificn. of antibodies

Cyclic peptides of formula (I) and their pharmaceutically acceptable salts are new; A = bond or a gp. NH-(CH2)-NCO; N = 1-11; B = bond or an alpha-aminoacid residue with 1 or 2 opt. O-contg. alkyl side chains, each of which can be substd. by 1 or 2 of 4-7C cycloalkyl-phenyl (opt substd. by e.g. NO2); naphthyl or a 5-6 membered aromatic heterocycle with 2N; are N plus one O or S; or one N, S or O; pref. thienyl, furyl, pyrrolyl, imidazolyl, pyrazolyl, pyridyl, pyrazinyl, pyrimidinyl, pyridazinyl, indolyl, (iso)quinolyl, chromanyl, thiazolyl, oxazolyl or morpholino; or A+B are together a peptide template; C = bond, Gly or alpha-aminoacid residue with 1 or 2 side chains at least one of which contains 1-4 N-contg. gps., D is as B but not a bond; E and F are each Gly or alpha-aminoacid residue in which the side chain contains no functional gps., or together they are NH-CH2)-MCO (M=2-11) or a peptide template; G is as C but not a bond; H = alpha amino acid residue which has 1 or 2 lipophilic side chains; I = bond or alpha amino acid residue in which the side chains contain (a) no functional gps. or (b) COOH or CONH2 as functional gps.; K is as G. L is as H.