Glycated haemoglobin, lipid peroxidation alternations in lipid composition and ATPase activities were analysed in erythrocyte plasma membrane of uncontrolled type II diabetes mellitus (DM) patients. Glycated haemoglobin, erythrocyte membrane cholesterol, phospholipid were significantly increased in DM patients. The molar ratio of cholesterol to phospholipid, lipid peroxidation in the form of thiobarbituric acid-reactive substances (TBARS), and Na+-K+-ATPase activity significantly decreased in the diabetic subjects, as compared to controls. The study suggested that biochemical changes in the erythrocyte membrane may be involved in the patho physiology of type II DM.