A model describing the hydroxyl radical (HO*) concentration pro. le at the boron-doped diamond (BDD) electrode, in the presence and absence of organic compounds, is presented. It is shown that this pro. le depends strongly on the reaction rate constant between the HO* and the organic compound. Furthermore, it is shown that the presence of organics affects the current-potential (I-V) curves. In fact, the higher the reaction rate between organics and HO*, the higher is the shift of the I-V curves toward lower potential with respect to oxygen evolution. Supposing that water discharge to free hydroxyl radicals on BDD is governed by Nernst equation, this shift of the I-V curves toward lower potentials has been calculated and compared with the experimental data obtained on BDD using two model compounds: methanol and formic acid. (C) 2008 Elsevier Ltd. All rights reserved.