Аннотация:One of the important characteristics of human blood is the fraction of erythrocytes, which by one reason or another have a reduced ability to deform passing through thin capillaries (the fraction of poorly deformable erythrocytes). Laser diffractometry is one of the convenient, fast and relatively simple techniques for measuring the erythrocytes deformability in blood samples. This technique allows for quick evaluation of the mean deformability of the erythrocytes. In this work, we present a new method of evaluation of the fraction of poorly deformable cells in erythrocyte suspension.