The reduction of OS to HO*-and the reverse process have been studied in alkaline solutions on pyrolytic carbon, porous carbon and graphite in which the pores have been tilled with para& in order to restrict the electrochemical reactions to the outermost surface, mainly by the rotating disk technique. With both types of carbon the cathodic polarization is a linear function of log [i/ (il -i)], where iJ is the diffusion limiting current density. The slope &,~/a log [i& -i)] is -0.11 to -0.15 per decade at 25°C for 0% pressures from 1 to 15 atm. The anodic measurements on the pan&n-tllled electrodes indicate a kinetically controlled limiting current density which is directly proportional to the HO*-concentration and independent of OH-concentration for 0.1 to 4.OM KOH. The anodic polarization is a linear function of log [i/& -i)] with an approximate slope of @12. The cathodic data support the hypothesis that the rate-determining step is an one-electron process leading to the formation of a peroxide-radical intermediate (O,-or 0J-T) which is probably adsorbed on the electrode surface. R&sum&Application de la mdthode du disque tournant a l'etude de la reduction de OS en HO, et son inverse, en solution alcaline sur carbone pyrolytique, carbone poreux ou graphite, dont les pores sont comblea au moyen de parafFine. Avec lea deux carbones, la polarisation cathodique est fonction linkire de log [i/iL -J], avec une pente de -0,ll a -0,15 a 25"C, pour des pressions d'oxygene comprises entre 1 et 15 atmospheres. Avec les electrodes comb&s, le courant anodique limite apparf& proportionnel a [HO,-] et ind+endant de [OH-] (en KOH. 0,l a 4,0 M); la polarisation anodique est aussi fonction lintaire de log [i/i& -i] avec une pente environ 0,12. Les r&mats cathodiques suggerent l'hypoth&se que p&ape r6gulatrice eat un processus n'impliquant qu'une electron et gennbrateur d'un radical peroxyde intermediaire (O,-ou O&T) adsorbable a la surface.