We are investigating the biological activities of analogues of oxytocin, the vasopressins, and somatostatin which incorporate amino acids other than the twenty commonly occurring ones. These amino acid surrogates were chosen to mimic steric factors of their natural analogues but to differ in their electronic parameters. Both solution and Merrifield solid phase methods are being utilized in our work; the precursor peptides to somatostatin will also be used in an nmr investigation of the conformational structures of somatostatin and these surrogate-containing analogues. Among the amino acids being substituted are Beta-chloroalamine, thioasparagine, thioglutamine and Beta-thiazolyl-alanine.