Somatostatin (SS) is modified to incorporate a carbohydrate moiety in the peptide chain by linkage to either Asn, Ser or Thr. The modified SS peptide analog may have the formula: ##STR1## wherein R.sub.1 is preferably a hexose or amino-hexose, such as glucose or N-acetylglucosamine. Alternatively, the carbohydrate can be linked to Ser or Thr by an ether bond. Such glycosomatostatins have an extended biological half-life compared to the parent peptide and substantially the same potency. Modifications and substitutions with respect to other amino acid residues in the chain can be made in the glycopeptides, for the purpose of increasing the effectiveness of SS analogs in other ways, and such increased effectiveness is a characteristic of the glycosomatostatin along with its longer-acting biological effect.