Abstract The redox process, Cl 2+2 e→ 2 Cl −, occurs reversibly on a platinized-platinum microelectrode with periodical renewal of the diffusion layer. the processes, Br 2+2e → 2 Br − and I 2+2e→2I − occur reversibly in 1 N HCIO 4 either on a smooth or platinized electrode. In 1 N Nano 3 the first of these reactions occurs only on a smooth electrode. the voltammetric curves obtained with a 5.10 −4 M Iodide solution in Hcl at a concentration between 1 and 10 −3 N (the ionic strength being kept constant by the addition Of HCIO 4) show two anodic waves of about the same height. the first wave is due to the oxidation of iodide ion to iodine, the second to the reaction 1 2+4 Cl −→ 2 ICl − 2 +2 e or I 2+2 Cl −→ ICl − +2 e, according to the activity of the chloride ion in the solution. the voltammetric curves obtained with 5.10 −4 M iodide ion in HBr at a concentration between 1 and 0.28 N show a single anodic wave corresponding to the oxidation, I − +2 Br − → IBr 2 − + 2 e. Decreasing the bromide ion concentration below 0.28 N causes a distortion of the wave and finally a splitting : the two waves thus obtained correspond to the oxidation reactions of iodide ion to iodine and of this iodine to IBr 2 − or to IBr. the reversibility of the various oxidation-reduction systems and also the E 1 2 -values of the corresponding waves as functions of the concentrations of halide ions, have been verified. a strict relation between the e 1 2 -potentials and the electrode characteristics has been established. The results are in very good agreement with the values calculated on the basis of the equation valid for spherical diffusion.