Compounds of the formula 1 or 1a ##STR1##HSCH.sub.2 CH(R)CO--Lys--Asn--Phe--Phe--Trp--Lys--Thr--Phe--Thr--Ser--NHCH.sub.2 CH.sub.2 SH (1a)In which R is hydrogen or NHR.sup.1 in which R.sup.1 is lower aliphatic acyl containing from 1 - 6 carbon atoms or benzoyl, and pharmaceutically acceptable salts thereof are disclosed. The compounds of formulae 1 and 1a are useful for the management of diabetes and the treatment of acromegaly in mammals. Methods for their use also are disclosed.