In experiments on cultured endothelial cells of human umbilical vein, we found that incubation of these cells during 24 hours with malondiaidehyde (cone. 200 microM) led to over two-fold increase in the cell stiffness. These data suggest that manifold augmentation of malondialdehyde concentration during oxidative stress may be accompanied by a considerable weakening of endothelium-dependent shear stress-induced arterial dilation.