The dynamics of sedimentation of whole blood cells and erythrocyte mass during sequential dilution with dextran solutions in vitro has been studied. Nonmonotonic changes in the optical density of the border between erythrocytes deposited both in their own plasma and in model systems were revealed. Fluctuations in the average and instantaneous rates of the process recorded at the boundary of cell subsidence confirm the nonlinear and cooperative nature of erythrocyte sedimentation, which is associated with the formation and separation of phases between cellular, liquid and gaseous components of blood. The structural reorganization of this dynamic system can be modulated in various ways, for example, by adding dextran solutions used in clinical practice in the case of blood loss, for detoxification, treatment and prevention of thrombophlebitis and shock conditions. It has been shown that the macro- and microkinetics of the erythrocyte sedimentation process depends both on the degree of dilution of blood (or model systems) by dextrans and on their molecular weight. The results obtained are consistent with the phase hypothesis of the settling of blood cells as a biocolloid, and can also be used in clinical hemotransfusiology to select an individual dosage of infusion solutions.