We examined the pharmacological properties of U-97018, a novel nonpeptide angiotensin II (AII) receptor antagonist, in various in vitro and in vivo studies. U-97018 selectively displaced 125I-AII specific binding in the membrane fraction derived from the rat mesenteric artery and adrenal cortex (AT1 subtype) with IC50 of 1.3 +/- 0.2 and 7.7 +/- 1.3 nM, respectively, without altering the AII binding of the rat adrenal medulla (AT2 subtype). In rat adrenal cortical cells, U-97018 inhibited 1 nM AII-induced aldosterone secretion with an IC50 of 0.48 nM; it shifted concentration-secretion response curve for AII to the right and inhibited the maximal response to AII, yielding a pKB of 9.8. Similarly, U-97018 showed insurmountable antagonism with a pKB of 10.6 against the AII-induced contraction in the isolated rabbit aorta. U-97018 had no direct effect on the activities of renin and angiotensin converting enzyme in vitro. In pithed rats, U-97018 inhibited the AII-induced pressor response with an ED50 of 0.28 mg/kg, i.v. without any partial agonistic activity. In anesthetized rats and dogs, intraduodenal administration of U-97018 at a dose of 1 mg/kg inhibited the AII-induced pressor response by about 60%. In spontaneously hypertensive rats, U-97018 at 10 mg/kg p.o. produced antihypertensive effects which lasted for 24 hr after administration. Thus, U-97018 is an orally active, insurmountable AII receptor antagonist without any agonistic activity.