It is demonstrated that Fe3+ in one solution can be reduced to Fe2+ by ascorbic acid in another solution when both aqueous solutions are separated by polyaniline membrane. This transmembrane redox process is possible due to electron/anion coupled counter transport through polyaniline membrane. It was demonstrated that at least one of the solutions must have acidic pH to initiate the transmembrane redox reaction. Both redox processes on the solution/membrane interfaces and the electron/ion coupled transport through the membrane play important role in determining the rate of transmembrane reaction. Possible kinetic mechanism is proposed. Apparent "diffusion coefficients" for redox equivalents inside polyaniline membrane and the rate constants of redox reactions on both solution/membrane interfaces are estimated. Maximal transmembrane reaction rate is 2 x 10(-9) mol/(s cm(2)) in terms of transport of redox equivalents through the membrane and formation of Fe (2+). This value is much higher than the typical values of the rates of respiration in mitochondria expressed in the same units. For thin membranes, the rates of transmembrane redox reactions are determined by interface processes and characteristic times are comparable to those in biomembranes.