Kallidin, a decapeptide with the sequence H-Lys-Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg-OH, is a bioactive kinin (peptide with an antihypertensive effect) belonging to the plasma kinins. It is formed from the precursor kallidinogen found in blood plasma by the protease kallikrein. It can be converted into bradykinin by the enzyme aminopeptidase.
In addition to its vasodilatory effect, it contracts the smooth muscles of the intestines, uterus and bronchi.