[Asp1, Val5, Ser9]angiotensin I was synthesized by Merrifield's solid-phase procedure. The dansylated derivative of this angiotensin was cochromatographed on the TLC with the dansylated angiotensin decapeptide isolated from white leghorn fowl. Either angiotensin showed identical behavior. The per mole pressor activity of the synthetic decapeptide (in rats anesthetized with pentobarbital and treated with pentolinium) as compared to mammalian angiotensins, namely, [Ile5]angiotensin I, [Val5]angiotensin I, [Ile5]angiotensin II, and [Val5]angiotensin II, was 157, 181, 114, and 85%, respectively.