The inhibitory effects of glipizide on cromakalim-induced relaxation of aortae and hypotension in the anesthetized rats was examined. In rat thoracic aortic rings pre-contracted with norepinephrine, cromakalim produced a relaxation sustainedly. This relaxation was completely inhibited by pre- or post-treatment of glipizide. In the anesthetized rat, cromakalim produced a rapid and sustained fall in the arterial blood pressure. This hypotensive action of cromakalim was abolished by pre- or post-treatment of glipizide. It is suggested that glipizide is the potent inhibitor of cromakalim, $K^{+}$ channel opener, in the rats.