Arterial and venous constriction during microsurgery are among the leading causes of flap failure. So far, pharmacologic tools have been proposed only for arterial constriction, and local anesthetics are commonly used to counteract the vascular spasm. The purpose of this study was to investigate the vascular effects of two known arterial vasodilators on human veins, in order to evaluate the possibility of their potential use during microsurgery. In vitro experiments were performed on 31 greater saphenous vein (SV) rings obtained from 20 patients and on 12 cephalic vein (CV) rings from 7 patients. The rings were mounted in organ baths and their isometric contractile activity was measured. Experiments were conducted by cumulatively adding calcitonin gene-related peptide (CGRP) or lidocaine to the organ baths. The endothelium was mechanically removed in 18 SV rings and in 6 CV rings. Results demonstrated that in vitro CGRP produced vasodilation only; no constrictive effects were seen. Lidocaine produced a biphasic response with contraction at low concentrations (1.5 x 10(-5) M, 1.5 x 10(-3) M) and release of the maximal contraction at higher concentrations, similar to that observed in arteries. Removal of the endothelium did not significantly affect contractile activity in either CGRP- or lidocaine-treated vessels. The data supported the conclusion that CGRP could be used to relieve venous constriction, and it is suggested that further studies on the clinical use of CGRP in microsurgery is warranted.