1. A renin-inhibitory material has been partially purified from soluble extracts of the pig kidney cortex by ammonium sulphate precipitation and diethylaminoethylcellulose (DEAE) chromatography and its properties studied.
2. It displayed competitive type kinetics. It did not inhibit cathepsin D, carboxypeptidase A, pancreatic kallikrein or trypsin.
3. Renins from dog, rabbit and rat were inhibited, but not those from sheep or man, when assayed with pig angiotensinogen.
4. The material was inactivated by treatment with trypsin, N-ethylmaleimide or p-chloromercuribenzoate.
5. Renin-inhibitory activity was not found in plasma from peripheral blood of pigs.
6. It is concluded that the function of the renin inhibitor in the renal cortex of the pig may be restricted to the intrarenal environment.