(D-Pro7)-Angiotensin I/II (1-7) is a potent Mas receptor inhibitor with a Ki of 0.001 µM for rat receptors. (D-Pro7)-Angiotensin I/II (1-7) competitively blocks the binding of Angiotensin-(1-7) to the Mas receptor and attenuates the vasodilatory effect of rat aortas under physiological and hypertensive conditions. (D-Pro7)-Angiotensin I/II (1-7) can be used for studies on the function of the renin-angiotensin system and the pathological mechanisms of hypertension[1][2].