The electrochemical methods, based on the polarographic discharge of a fast redox-system, are applied to the blood medium in order to study the process of exchange of matter. The measurements of the limiting diffusion current and of the electrochemical impedance are carried out with the help of a rotating disc electrode. It could be shown that the ferrocene-ferricinium couple, selected as a diffusion tracer, provides information on the erythrocytic, membrane, on the diffusion coefficients, and on the rheology of the medium.