To study the correlation between the activity of Na+-K+ -ATPase on erythrocyte membrane and arteriosclerotic cerebral infarction. Activity of Na+-K+ -ATPase on erythrocyte membrane was determined in 37 cases of arteriosclerotic cerebral infarction (ACI)and 25 normal control subjects. Activity of Na+ -K+-ATPase on erythrocyte membrane in ACI was obviously lower than that of control (P<0. 001), and the activity of Na+ -K+ -ATPase on erythrocyte membrane was negative correlated with infarct size on brain CT scans in ACI(r= -0. 58, P<0. 01).It suggested that the reduced activity of Na+ -K +-ATPase on erythrocyte membrane may have some ef-fect in the development of ACI.