In a group of 36 homozigous beta-thalassaemic children we studied the effect of splenectomy on hemorheologic characteristics. The aim of the work was to evaluate the importance of such operation either on anemia or on erythrocyte deformability. Whole blood viscosity was measured with a Brookfield Microviscometer (LVT) and erythrocyte deformability was evaluated with the erythrocyte filtration technique using policarbonate membranes. The more the erythrocyte deformability decreases, the more the erythrocyte filtration rate decreases. Our data show that splenectomized children, have worse hemorheologic characteristics according to the longer survival time of pathological red blood cells in spite of their reduced deformability. This behaviour can be modified only by blood transfusion that we have seen to be able to reduce whole blood viscosity and to increase erythrocyte filtration rate in splenectomized children. We think that splenectomy must be delayed as long as possible so that hemodinamyc conditions cannot be worsened. An hemorheologic monitorage could be useful for diagnostic and prognostic evaluations both in splenectomized and not splenectomized children.