34 halogen 34 or 34 halo 34 is intended to include fluorine chlorine bromine and iodine the term 34 5 or 6 membered heterocyclic ring 34 is intended to include those 5 and 6 membered heterocycles with 1 or 2 heteroatoms selected from oxygen nitrogen and sulfur exemplary of such heterocycles is imidazole furan thiazole pyrazole pyridine and the like in the instant compounds there are several assymetric centers which will lead to the existence of optical isomers for such compounds in the instant invention for each of the assymetric centers of the various amino acids which make up the instant cyclic hexapeptides both the d and l configurations as well as diastereomers therein included are intended to be encompassed it will be appreciated by those skilled in the art that when r 1 and r 2 are benzyl r 3 is indolylmethyl y 1 and y 2 are hydrogen and r 4 is 1 hydroxyethyl the 7 8 9 10 and 11 amino acids of somatostatin phe trp lys thr phe are represented and the secondary amino acid represented by n methyl alanine when r 5 is methyl and by proline when x is methylene has taken the place of the remainder of the somatostatin amino acids thus using the above definitions of the substituent groups the following representative cyclic hexapeptide analogs of somatostatin are formed str3 the preferred embodiments of the cyclic hexapeptides of this invention.