(1) The renin-angiotensinogen reaction has been utilized to determine the renin in small specimens of kidney tissue.
(2) The pretreatment of rat or human kidney extract at pH 3.0, 0°C, for 30 min. gave a reliable method to remove angiotensinase.
(3) The pretreated extract of various concentrations was reacted on the plasma at pH 6.5, 37°C, for 10 min.
(4) Angiotensin thus formed was determined by its pressor action in the rat anesthetized by pentobarbital and treated by pentolinium.
(5) It was shown that, to express the amount of renin, the reaction con-stant (K) as expressed per original concentration of the kidney extract and per min. may be used.
(6) The method is applicable to as little as 0.01 Gm. of renal tissue.