Polyaniline (PANI) was prepared electrochemically by the pulse and potentialrncycling methods at gold and platinum electrodes, respectively. Thin and thick films werernprepared by the latter method. Square-wave and ac-voltammetric methods were employed torninvestigate the leucoemeraldine/emeraldine redox couple. Two well-separated cunent peaksrnwere obse!ved in the thick films suggesting a two-step reaction in the oxidation process. Therneffect of supporting electrolytes on the ac-voltammetric behavior of PANI was alsorninvestigated. The positions of the current peaks seem to be influenced by the size of thernanion. The obselved two-current peaks might be due to a two-step reaction in therntransformation of leucoemeraldine to emeraldine.