Abstract: New hypocalcaemic peptides are disclosed of the formula ##STR1## wherein X represents H for the replacement of the N alpha amino group or acyl groups for the acylation of the N alpha amino group, the N-alpha amino group. The acyl groups are carboxylic acids especially formic, acetic, propionic, buteric, valeric, hexanoic, heptanoic, octanoic, and nonanoic acids or their respective isomers, L-lactic acid and the half amides of malonic, succinic, glutaric and adipic acids. Y is L-valine, glycine, L-methionine, L-alanine, L-leucine or L-isoleucine.

Abstract: New peptides are disclosed which have biological activity of the same type as known calcitonins and which do not have a leucine in position 19 or a glutamine in position 20. Both amino acids are omitted. Also resin peptides are disclosed which may be converted to peptides having such biological activity; and processes for producing said resin peptides and said calcitonin peptides.

Abstract: New peptides are disclosed which have biological activity of the same type as known calcitonins and which do not have a disulfide bond connecting the cysteines at positions one and seven. Also resin peptides are disclosed which may be converted to peptides having such biological activity; and processes for producing said resin peptides and said calcitonin partially protected peptides.