Аннотация:The problem of measuring red blood cell deformability by laser diffractometry in a shear flow (ektacytome¬try) is considered. New data processing algorithm is proposed to measure the variance of the erythrocyte deformability. This algorithm is valid for slightly inhomogeneous ensemble of erythrocytes with a symmetrical distribution in deformability. The algorithm uses part of the diffraction pattern which is the most sensitive to the erythrocyte characteristics. An attractive feature of the algorithm is that it needs only geometrical parameters of the diffraction pattern but does not require measurement its energy parameters.