The hemorheological effects of autologous blood storage with or without the use of erythropoietin were examined before surgery for valvular disease. There was no rheological difference between patients with aortic (16 cases) or mitral (10 cases) valve disease. Before storage, the levels of hematocrit, whole blood viscosity, and especially coefficient of rheology, were lower (p< 0.05) in the blood stored with erythropoietin, but this difference disappeared after storage. The plasma viscosity of both groups did not change before and after storage. The viscosity of blood was equalized after the storage of blood, irrespective of the use of erythropoietin.