Abstract: A method for the determination of（Ca,Mg）-ATPase activity on human erythrocyte menbranes was established,and its preliminary clinical use was reported.The erythrocyte membrane(Ca, Mg(-ATPase was assayed in 81 normal subjects and 35 patients with various diseases.Reduction of（Ca,Mg）-ATPase activity was found in patient with Duchenne muscular dystrophy,myocardial infarction and renal failure.The result suggests that erythrocyte membrane defects may be present in these diseases.