Abstract: Effects of antihypertensive factor （AHF） from erythrocytes of human beings, rats, rabbits and dogs on the blood pressure （BP ） in rats were studied. Cornparative studies on the dcpressor effects of AHF from the heart, liver. kidney.brain and erythrocytes of rats were also investigated. The results showed that AHF from red blood cell （RBC ） of human beings and the animals at the doses of 0. 01, 0. 1 or 1. 0（mg/ kg） significantly decreased BP of rat in a dose-dependent manner. The AHF from erythrocyte had a greater depressor effect than preparation equivalent concentration of tissue extracts.AHF from RBC of the different animals at the doses of 40μg/ ml caused a sustained relaxation on phenylephrine-preconstricted rat aortic rings. Known vasoactive substance blockers could not alter the effect of AHF on BP. These data indicated that the effect of AHF on BP might be mediated via a specific receptor.