[en] Analysis of the electrochemical phenomena arising in the processes of extraction-reextraction demonstrated that they are followed by interphase potential difference which can reach a few hundreds millivolt. During mass transfer across the phase boundary of the extragent ((C₄H₉O)₃PO, R₃PO, [CH₃(CH₂)₇]₃N and others in dissolvent) and aqueous solution, potential difference of the same kind as diffusion potentials at the boundary of the solutions with different concentrations and distinguishing movability of the ions opposite charged occur in both phases. (author)