Diphenylcarbazide (DPCI) or diphenylcarbazone (DPCO) is introduced into carbon paste electrodes in order to determine the potential ranges where the oxidation-reduction processes of these species occur in 0.3 M HClO4, The potential controlled electrolysis was performed for DPCI and DPCO dissolved in 0.3 M HClO4. From the coulometric results and the UV-visible spectral data of the solution before and after the electrolysis it is possible to establish that DPCI is oxidized in an irreversible process giving diphenylcarbadiazone (DPCDO). DPCO is probably an intermediate in this oxidation, but its concentration is never high because it is slightly more easily oxidized than DPCI, DPCO can be reduced to DPCI at about 0.2 V (ECS) and, finally, DPCDO can be reduced to DPCI at about - 0.5 V (ECS), Again, DPCO is probably an intermediate but is not detected because it is so much more easily reduced than DPCDO.