C-type Natriuretic Peptide (CNP), identified in 1990 and called C-type (in order to maintain the alphabetical nomenclature of natriuretic peptides), is the most highly conserved of natriuretic peptides between species. It is derived from a 126 amino acid preprohormone. CNP exists in two mature forms, one found in tissues, another in plasma and cerebrospinal fluid. It is present in high concentration of the vascular tree, especially the endothelium, central nervous tissues, and renal tubular cells. It is a powerful vasorelaxant and inhibitor of smooth muscle cell proliferation and may play a role in coagulation and fibrinogenesis by modulating endothelial cells.