Results of the study of 19 purine derivatives by cyclic voltammetry and conventional polarography are compared with those obtained earlier by oscillographic polarography. The reduction product which is formed at mercury electrodes polarized to high negative potentials in the region of the background discharge and which gives rise to an anodic reaction at about —0.2 v. is yielded only with those purine derivatives which are substituted at the 2 and 6 positions, are nonreducible under normal polarographic conditions (with the exception of 2,6-diaminopurine) and which of the 7 and 8 positions are not occupied. The reduction product is very unstable and a chemical step preceding the anodic reaction is suggested.