AbstractA type-dependent chemotoxic effect of radiographic contrast media on erythrocytes and endothelial cells was reported several times. While mechanisms of toxicity are still unclear the cellular reactions e.g. echinocyte formation in erythrocytes and the buckling of endothelial cells coincided with deterioration of capillary perfusion (in patients with coronary artery disease) and tissue oxygen tension (in the myocardium of pigs). Whether the shape changes in erythrocytes coincide with changes in the arrangement of actin, the core of the actin-spectrin cytoskeletal network and possible actor in membrane stresses and deformation is not known until now. To get specific informations actin was stained using two different staining methods (antibodies to β-actin staining oligomeric G-actin and polymeric F-actin and Phalloidin-Rhodamin staining polymeric F-actin only). In addition, an advanced version of confocal laser scanning microscopes was used enabling the display of the actin arrangement near substrate surfaces. Blood smears were produced after erythrocyte suspension in autologous plasma or in two different plasma/RCM mixtures. In this study an even homogenous distribution of fine grained globular actin in the normal human erythrocyte could be demonstrated. After suspension of erythrocytes in a plasma/Iodixanol mixture an increased number of membrane protrusions appeared densely filled with intensely stained actin similar to cells suspended in autologous plasma, however, there in less numbers. Suspension in Iopromide, in contrast, induced a complete reorganization of the cytoskeletal actin: the fine grained globular actin distribution disappeared and only few, long and thick actin filaments bundled and possibly polymerized appeared, instead, shown here for the first time.