The pharmacological properties of three antagonists of angiotensin II (ATII) have been characterized on the rat isolated stomach strip.(8-Gly)-ATII, a newly synthesized antagonist of ATII, as well as (8-Leu)-ATII and (1-Sar-8-Leu)-ATII displace to the right the dose–response curve of ATII and the displacement is proportional to the dose of antagonist.Dose–response curves of ATII remain parallel to that of the control in the presence of (8-Gly)-ATII and (8-Leu)-ATII, while parallelism is lost with (1-Sar-8-Leu)-ATII. This antagonist also depresses the maximal response to ATII.All data presented in this paper indicate that (8-Gly)-ATII and (8-Leu)-ATII are competitive antagonists of ATII with different affinities for the receptors, (8-Gly)-ATII being about 12 times less potent than (8-Leu)-ATII. This compound competes with ATII on a one to one basis: pA2 of (8-Leu)-ATII has the same value as pD2 of ATII.(1-Sar-8-Leu)-ATII does not fulfil the criteria of a competitive antagonist. This compound is very potent and the onset of action is as rapid (5 min) as for the other two compounds. All data obtained with (1-Sar-8-Leu)-ATII are consistent with the assumption that this compound is competitive in the sense that it acts on the same receptor site as ATII, but owing probably to slow rate of inactivation by tissue aminopeptidases, it dissociates slowly from the receptors and it acts as a specific long-acting antagonist.