The vasodilative effect of perillaldehyde, one of the major oil components in Perilla frutescens BRITTON, was studied using isolated rat aorta. Perillaldehyde at final concentrations of 0.01 to 1 mM showed dose-dependent relaxation of the aorta contracted by treatment with prostaglandin F2alpha or norepinephrine. Neither the presence of NG-nitro-L-arginine methyl ester nor removal of the aortic endothelium affected the vasodilatation, suggesting that perillaldehyde exerts a direct effect on vascular smooth muscle cells. The vasodilative effect of perillaldehyde was not inhibited by pretreatment with a beta-adrenergic receptor blocker (propranolol), an inhibitor of phosphodiesterase (theophylline), a delayed rectifier K+ channel blocker (tetraethylammonium chloride), or an ATP-sensitive K+ channel blocker (glibenclamide). However, perillaldehyde showed contrasting effects on vasodilatation of the aorta contracted by an influx of extracellular Ca2+ - perillaldehyde caused little vasodilatation on the aorta contracted by the Ca2+ ionophore A23187, while it inhibited the vasoconstriction induced by treatment with high-concentration K+, which dominantly opened the voltage-dependent Ca2+ channel. These results suggest that the vasodilative effect of perillaldehyde is derived from blocking the Ca2+ channels.