The present study was performed to test the effect of trapidil on superficial veins in healthy subjects using the dorsal hand vein compliance technique. In study A in a cross-over design trapidil was infused into a dorsal hand vein wich was preconstricted by local infusion of either norepinephrine or dinoprost. At the beginning of each test the individual dose of norepinephrine or dinoprost that produced about 80% constriction was determined by infusion of ascending dosages of norepinephrine or dinoprost. This dose of norepinephrine or dinoprost was then infused at a constant rate during the subsequent infusion of ascending dosages of trapidil. Local infusion of trapidil induced a dose-dependent dilation of preconstricted dorsal hand veins. The results show that trapidil is able to inhibit the vasoconstrictive effect of norepinephrine on the human hand vein as well as that of dinoprost wich is a non-adrenergic vasoconstrictor. In study B the influence of an oral dose of trapidil (200 mg) and of placebo on norepinephrin-induced venoconstriction has been investigated in in healthy male volunteers, also using the dorsal hand vein compliance technique. The dose-response curves for venoconstriction by locally infused norepinephrine were established before and 1 h, 2 h and 3 h after oral medication. The comparison of the mean ED50-values of norepinephrine show that the norepinephrine effect weakened after the medication of placebo and that oral administration in contrast to lokal intravenous administration of trapidil did not diminish a peripheral venoconstriction but increases it slightly, perhaps reflectory to dilatation of large vessels.