The preparation of crystalline rennin previously described (1) was somewhat long and inconvenient, but the knowledge gained about the properties of the crystals suggested that a simpler method might be successful. Since then Møgensen (2) has shown that the mere precipitation of commercial rennet with saturated sodium chloride gives a product with proteolytic properties resembling those of the crystalline material, and with enhanced milk-clotting activity per unit of dry weight. Some years previously, Hankinson (3) had also achieved considerable purification by these means. The results of an attempt to discover a simple method of crystallization are described below.