1. We separated inactive renin in human plasma into two types, adsorbed and non-adsorbed, by chromatography on a concanavalin A-Sepharose column. About 75% of fresh plasma inactive renin was adsorbed to the column, and the rest passed through it. Non-adsorbed and adsorbed inactive renins were partially purified. 2. Non-adsorbed inactive renin had a molecular weight of 48000 and an isoelectric point of 5.44. Adsorbed inactive renin had a molecular weight of 46000 and isoelectric points of 5.56 and 5.80. 3. After activation with trypsin, both activated inactive renins were similar with respect to molecular weight (45000), thermostability, K m value (0.56 μmol/l) and pH profile. But pI values of both activated inactive renins differed. 4. These results indicate that there exist in human plasma two different types of inactive renin which differ in carbohydrate composition.