A new method of purification of renin is described. This method employs the following procedures: ethanol precipitation; saline extraction; precipitation of renin with 40% ammonium sulphate; precipitation of impurities with 3% ammonium sulphate at pH2.5; chromatography on DEAE-cellulose and CM-Sephadex; gel filtration on Sephadex G-100 (both normal and superfine grade); finally, starch-gel electrophoresis. 2. The final renin preparation had a specific activity 10(4) times that of the initial saline extract. 3. A single band of stained protein corresponding to the renin activity was present on starch-gel electrophoresis in the final step and a single precipitin line was obtained to this material with rabbit anti-(pig renin) serum. 4. Double diffusion in agar with rabbit anti-(pig renin) serum showed one major precipitin line, probably due to renin-anti-renin complex, and in addition two minor components.
