Abstract The electro-oxidation behavior of p-aminodiphenylamine (PADPA) in acetonitrile was investigated using cyclic voltammetry and controlled potential electrolysis. PADPA is oxidized in two steps in this medium. When the experiment is carried out in the presence of an equivalent amount of pyridine the second oxidation peak disappears. The first oxidation peak vanishes when the solution contains an equivalent amount of anhydrous perchloric acid. An intermediate oxidation peak which is due to the formation of the cation radical appears under certain conditions. The results are interpreted especially in relation to the role of this compound in the formation of polyaniline and a detailed mechanism is proposed.