Аннотация:Ischemic diseases of people and animals are accompanied with deterioration of microrheologic properties of their blood, in particular, with impairing red blood cells (RBC) deformability. In this work, the analysis of human and rat RBC deformability in norm and ischemia was performed by means of the laser diffractometry - a modern technique allowing for measuring the flexibility of RBC, which determines the blood flow parameters in vessels. Human RBC were obtained from the blood of healthy individuals and from patients suffering from ischemic diseases. Human RBC deformability from both groups of individuals was measured. Rat RBC were obtained from a control group of animals and from a group with experimentally induced ischemia (EII). This animal model is frequently used for studying the response of an organism to ischemia. The effect of Semax , a medication that is frequently used for therapeutic treatments of human brain diseases in clinical practice, on RBC deformability was studied with its application in vitro and in vivo. It is shown that in human ischemic patients, the deformability of RBC was lower than that from healthy individuals. Both in vivo and in vitro applied semax positively influences the impaired deformability properties of RBC of ischemic rats.