BIBS 39 is a new nonpeptide angiotensin II (AII) receptor antagonist. Target: Angiotensin Receptor in vitro: BIBS 39 displaces [125I] AII from its specific binding sites with a Ki value of 29 ± 7 nM for the AII subtype 1 (AT1) receptor and a Ki value of 480 ± 110 nM for the AII subtype 2 (AT2) receptor. BIBS 222 shows a Ki value of 20 ± 7 nM for the AT1 subtype and a Ki value of 730 ± 170 nM for the AT2 subtype. BIBS 39 is 17 times more selective for the AT1 subtype and BIBS 222 37 times. BIBS 39 shifts the AII concentration-contractile response curves in isolated rabbit aorta to the right in a parallel fashion. [1] in vivo: In pithed rats, BIBS 39 dependently shifts the dose-response curve of AII to the right without affecting the maximal response. BIBS 222 also causes parallel shifts to the right but a significant reduction of the maximal responses was observed at 3 and 10 mg/kg i.v. These results show that the benzimidazole derivatives BIBS 39 is a potent and selective AII receptor antagonists. Substitution with a benzimidazole moiety results into a considerable loss of selectivity for the AT1 receptor subtype compared with an imidazole moiety as, for instance, in DuP 753.[1] BIBS 39 is a new nonpeptide angiotensin receptor blockers that has affinity for both AT1- and AT2-receptors, is also a potent antagonist of the cardiovascular effects of AII in pithed rabbits. [2]