The preparation of rabbit renin-substrate for the assay of minute amounts of renin.

1. By DEAE-cellulose chromatography and treatment with Cd(2+) a partially purified renin-substrate has been prepared from rabbit serum. 2. It has the following properties: (a) Angiotensinase activity is undetectable: 0.1mug. of angiotensin was recovered intact after incubation with the substrate at 37 degrees for 200hr. (b) It does not contain renin and does not generate vaso-active substances when incubated alone. (c) It is ten times as active as serum in terms of angiotensin produced/mg. of protein. (d) It has not deteriorated after storage for 3 months at 4 degrees at pH7.5.