To study an aggregation of formed blood cells a setup is proposed in which use is made of the conductometric method of measuring the resistance of a fine-pore filter through which the blood passes. A specially devised sensor allows it also to study the process of the cells aggregation in the vascular system of test animals and to control the dispersion of formed cells in the apparatus of extracoporeal circulation. Among advantages offered by the method are the objective character of measurement, the possibility of investigating the whole blood and due consideration of the part played by hydrodynamic factors.