Calcitonin gene-related peptide (CGRP) produced a dose-related wheal and flare reaction in human skin at doses of 12.5 to 50 pmol. The flare response but not the wheal response to CGRP and substance P were inhibited by prior treatment of the subject with oral chlorpheniramine, 16 mg. CGRP, but not substance P, was potent in producing a delayed erythema and surrounding pallor in human skin, which peaked at 1 h and persisted for more than 3 h after injection, when wheal and flare responses had subsided. The delayed response was accompanied by infiltration of polymorphonuclear leukocytes. The delayed erythema and pallor produced in response to CGRP were not inhibited by oral chlorpheniramine, or by 4% prilocaine injected locally. CGRP released histamine from rat peritoneal mast cells over the concentration range 2.5-10 microM. CGRP was about fourfold less potent than substance P in releasing histamine. The substance P analogue, [D-Pro4, D-Trp7,9,10]SP4-11 10 microM, and benzalkonium chloride 10 microM inhibited histamine release from rat mast cells stimulated by either CGRP or substance P.