The radiolysis of potassium permanganate solutions is studied by means of a double tracer technique and a new analytical procedure in parallel with an ESR investigation. In this way it has been possible to determine without doubt that the only radiolytic product formed is MnO2in neutral solutions and Mn (II) in acid solutions. In the latter case Mn (II), at least to a major part, appears to accumulate after the end of the irradiation. At the same time it disappears, oxidized by permanganate. Several suggestions are advanced to explain this radiolytic and post-irradiation behaviour.