A heptacosapeptide having the following structural formula: Boc-His(Boc)-Ser(But)-Asp(OBut)-Gly-Thr(But)-Phe-Thr(But)-Ser(But)-Glu (OBut)-Leu-Ser(But)-Arg(X)-Leu-Arg(X)-Asp(OBut)-Ser(But)-Ala-Arg(X)-Le u-Gln-Arg(X)-Leu-Leu-Gln-Gly-Leu-Val-NH2, in which X is a group having the formula: <IMAGE> where R is an alkyl or alkoxy and m is an integer of 1 to 3, provided that R's may be the same or different in case m is 2 or 3. The heptacosapeptide may be converted to a secretin.
