Electrostatic repulsion among erythrocytes in flow was evaluated through measurement of the thickness of the marginal cell‐free layer in narrow glass tubes of 20–50
$\mu$
m in inner diameter. To reduce the electrostatic repulsive force, due mainly to sialic acid of the membrane glycoproteins, human erythrocytes were treated with neuraminidase. The surface negative charge of the erythrocytes, as determined from the electrophoretic mobility using free‐flow electrophoresis, was found to be proportional to the sialic acid content. When erythrocytes with decreased sialic acid content flowed through narrow tubes, the thickness of cell‐free layer determined using an image processor increased even in the absence of erythrocyte aggregation in the suspension. The effect was more pronounced at acidic pH. The addition of Dextran T‐70 (70,400 Mol. Wt.) further increased the cell‐free layer thickness due to erythrocyte aggregation. Thus, reducing the negative charge density on the erythrocyte surface by itself accelerates the axial accumulation of erythrocytes in flow due to the decreased electrostatic repulsive force between the cells, even in the absence of erythrocyte aggregation.
