The C-terminal fragment of the human alpha-calcitonin gene-related peptide (hCGRP), hCGRP-(8-37) competitively antagonized both the positive inotropic effect of hCGRP in the guinea-pig isolated left atria (pA2 6.89) and the smooth muscle relaxant effect of hCGRP in the rat isolated vas deferens (pA2 6.55) but left the response to isoprenaline unaffected in both preparations. In addition, hCGRP-(8-37) reduced the responses produced by activation of the 'efferent' function of capsaicin-sensitive primary afferents in both preparations thus providing pharmacological evidence for the involvement of endogenous CGRP. hCGRP-(8-37) appears a useful tool to establish the physiological role of CGRP in peripheral preparations from different species.