In cardiovascular disease the flow adaptation of erythrocytes can be affected by reduced shear stresses and metabolic influences on red cell fluidity as a consequence of tissue hypoxia. In addition there are indications that risk factors of cardiovascular diseases are able to decrease the intrinsic red cell deformability. Erythrocyte deformability was studied by the filtration technique of Reid et al. to investigate the relationship between blood pressure chances and erythrocyte deformability. In this experiment normotensive rats, spontaneously and DOCA-salt treated hypertensive rats were used. Erythrocyte deformability was significantly reduced by blood pressure elevation in hypertensive rats but was not fully recovered by normalization of blood pressure after antihypertensive drug treatment. Therefore other factors than blood pressure may be involved in erythrocyte deformability reduction during blood pressure elevation.