Angiotensins are peptide hormone components of the renin-angiotensin system involved in the regulation of blood vessel constriction and aldosterone release. Angiotensin I, a decapeptide derived from angiotensinogen, is a converted to Angiotensin II by the removal of the two C-terminal amino acids. Various analogues of Angiotensins I and II made by amino acid substitution are used in structure and sequence studies to analyze and differentiate the functions of natural angiotensins.