Tn order to understand the complex reduction mechanism of pertechnetate ions on mercury electrode we have developed electrochemical techniques which use an additional time parameter to the classical methods applied on mercury microelectrode: 3 Dimensional polarography and 3D differential capacity measurements have been investigated in addition with coulometry, cyclic voltammetry, and radioactivity determinations. We have concluded that the first VII --> III reduction wave, which has been described in literature, has to be associated with the successive VII --> V reactions followed by the disproportionation of Tc(V) and formation of Tc(VI) and insoluble tetravalent species which are adsorbed on the electrode and reduced to trivalent ions. Then, reduction of Tc(III) to Tc(0) is reached through Tc(II) and Tc(I) intermediate species. The intermediates are characterised depending on the time window of observation.