We present a study which reveals that the switching speed for the redox reaction of polyaniline is very fast. With a 1200Å film in 2M sulfuric acid, switching speeds of up to 100 µs with current densities of 100 A/cm2 are observed with the appropriate compensation for IR loss. The true switching speed is higher still and has not been measured. The oxidation and reduction processes have different electrical behaviors. For the reduction process, the reaction is controlled by the RC constant of the cell given by the resistance of the solution and the capacitance of the double layer. The oxidation process is more complicated and a full description is lacking. © 1989, The Electrochemical Society, Inc. All rights reserved.