The physicochemical properties of MA-40 and MA-41 ion-exchange membranes have been studied in two systems with different electrolyte compositions. The following test systems have been chosen for the study: anion-exchange membrane/mixed solution of sodium hydroxide and sodium naphthenate and anion-exchange membrane/mixed solution of sodium sulfate and sodium nitrate. Ion-exchange sorption and electrical conductivity have been studied in these systems. It has been found that both of the membranes are more selective for hydroxide ions than for naphthenic acid anions in the system with sodium naphthenate. A conductor-insulator percolation transition has been observed in the M?-40 and MA-41 membranes saturated with organic counterions. The mobilities and diffusion coefficients of hydroxide, nitrate, and sulfate ions in the test membranes haves been calculated.