This study on the enzymic activity consists of two parts, i. e., the experiment in vitro and in vivo. The enzyme materials in vitro experiment are the suspension of erythrocytes of some animals (goat, dog, rabbit and man), and to this suspension phenylhydrazine hydrochloride, potassium cyanide or potassium perchloride are added, otherwise the suspension is treated ultrasonically, through which the Heinz's granules have been induced to appear in the erythrocytes of the suspension. The materials in vivo experiment are also the suspension of rabbit's erythrocytes, which have been subcutaneously injected or orally given phenylhydrazine hydrochloride or p-nitroaniline, causing the Heinz's granules to form in the erythrocytes of the suspension. For both experiments in vitro and in vivo the suspension of the Heinz's-granule-free erythrocytes from the normal animals are used as the control. The author has examined the activity of cathepsin (by estimation of non-protein nitrogen), of cholinesterase as well as of lipase (by estimation of CO(2) with Warburg's manometer), and of phosphatase (by estimation of H(3)PO(4)) of the both enzyme materials. The followings are the results: 1) The activity of cathepsin, cholinesterase, and lipase of the erythrocytes showing Heinz's granules had increased in both experiments in vitro and in vivo. 2) The activity of phosphatase of the erythrocytes with Heinz's granules had decreased when compared with that of the normal erythrocytes (control) in vitro experiment, but it was increased in vivo. 3) If the Heinz's bodies have been induced to appear in erytrocytes in the same way, the higher the number (%) of such erythrocytes in the suspension become, the more remarkable is the increase or the decrease of the activity of the said four enzymes of the erythrocytes with the Heinz's granules. When the methods of demonstrating the Heinz's granules in erythrocytes are different, the increase or decrease of the activity of the respective enzyme are not necessarily equal even the number(%) of the erythrocytes with the Heinz's bodies is the same.