Claimed are a series of somatostatin agonists and uses thereof, according to formula (I), A.sup.1-cyclo[Cys-A.sup.2-D-Trp-A.sup.3-A.sup.4-Cys]-A.sup.5-Y.sup.1, (I) wherein A.sup.1, A.sup.2, A.sup.3, A.sup.4, A.sup.5 and Y.sup.1 are as defined in specification provided that the amine nitrogen of at least one peptide bond is substituted with a methyl group or pharmaceutically acceptable salts thereof.