The calcitonin gene has been shown to give rise to another peptide, calcitonin gene-related peptide (CGRP). The structure of human CGRP has been determined by mass spectrometry. Calcitonin gene-related peptide-containing neurons have been detected in a number of species, particularly in association with heart and blood vessels. Pharmacological studies have shown that CGRP is a potent vasodilator in a number of vessels and vascular beds, including the skin and coronary circulation. Investigations in humans have also reported the potent vasodilator action of CGRP. The evidence from these studies suggests that CGRP is an important regulator of vascular tone and blood flow.