The levels of the three ATPases found in the erythrocyte membrane of diabetic patients were significantly lower than normal subjects. The distribution of the enzymes was also different. Na+,K+-ATPase and Mg2+-ATPase reflected the status of blood glucose more than Ca2+-ATPase. The ratio between two of the ATPases was sensitive to glycemic response. When dikanut, a viscous preparation, was fed to diabetics for 4 weeks, blood glucose became normal and the activities of the three ATPases increased significantly. The ratio among the enzymes also approached that of normal subjects. A relationship was found between the blood glucose level and erythrocyte membrane ATPases which, if linked to insulin binding or level, may provide a rapid inexpensive assay in diabetes research.