A recently predicted form of human calcitonin gene-related peptide, (beta CGRP) exhibits potent vasodilator activity in rabbit skin with a similar potency to the form of human CGRP originally described (alpha CGRP). Both peptides, because of their vasodilator activity, cause a potentiation of inflammatory oedema induced by mediators of increased vascular permeability. The results demonstrate that changes can be made at certain positions in the amino acid sequence of human CGRP without loss of vasodilator activity.