A monoclonal antibody specific for the carboxy-terminus of angiotensin II was produced from the somatic cell fusion between SP2/0 myeloma cells and spleen cells from CAF/J mice immunized with angiotensin II selectively coupled to thyroglobulin. The subcloned line D5-7R2 was augmented in the ascites form and shown to be specific for angiotensin II (octapeptide) and shorter angiotensin peptides. This antibody, however, did not cross-react with angiotensin I (decapeptide). This selectivity will be important in clinical assays that measure angiotensin II in the presence of angiotensin I.