The invention relates to medical technology and can be used in extracorporeal blood purification therapy for plasmapheresis, plasma exchange and cascade filtration of blood. A method for blood plasma exchange is proposed, in a known method of phase-selective extraction, including counterflow convective mass transfer between a suspension (blood) channel and two adjacent channels with permeable walls for a solution during alternation of cycles with alternating pressure differentials between the channels, wherein during these cycles, the blood supply is cut off and the inlet and outlet of the blood channel are closed and in between these cycles, an additional cycle is carried out, during which the solution supply is cut off and the inlets and outlets of the solution channels are closed, and the inlet and outlet of the blood channel are opened for the flow of blood. In order to displace the blood in the additional cycle, pumping devices are used, or displacement is carried out as a result of the difference in the levels of the blood at the inlet and the outlet. In order to obtain low values for the degree of plasma exchange, but plasma which is less diluted by the solution, the ratio of the average solution flow rate for the four cycles to the equivalent blood flow rate is set from a range of 0.001 to 1.0. In order to obtain high values for the degree of plasma exchange, but plasma which is more diluted by the solution, the ratio of the average solution flow rate for the four cycles to the equivalent blood flow rate is set at more than 2.0. The volume of blood supplied to the additional cycles is set at no more than the volume of the blood channel. The solution and the blood can be supplied in a forward flow.Linvention se rapporte au domaine des techniques médicales et peut être utilisée en thérapie efférente de plasmaphérèse, de remplacement de plasma et de filtration sanguine en cascade. Linvention concerne un procédé de remplacement de plasma sanguin, dans le cadre
