The Cl2 evolution reaction was studied at highly boron-doped diamond thin film electrodes. The comparison of this carbonaceous material with graphite and glassy carbon points out the similar behavior in terms of diagnostic parameters and related mechanisms, without the mech. fragility of these materials. Tafel slopes at different chloride concns. in soln. (from 0.1-4 M NaCl in 0.01 M HClO4) and at different pHs were detd., together with the reaction orders with respect to Cl- and H+. All measurements were carried out at a const. ionic strength. The electrode characterization was done by cyclic voltammetry, showing a detailed picture for the chloride oxidn. and the redn. of the evolved Cl2. Significant surface modifications occur when the electrode works as an anode for oxygen evolution, while Cl2 evolution does not seem to cause severe changes. As shown by tests carried out following a method suggested in the literature, the faradaic yield for Cl2 prodn. is expected to be very high. In dil. chloride media and at neutral-weakly alk. pH, a faradaic yield of ~65% was found; this makes use of highly doped diamond electrodes in, e.g., seawater electrolysis, quite promising. [on SciFinder (R)]