The paper presents the results on the evolution of electronic features and electrochemical activity of boron doped diamond samples during oxidative ageing tests. For 1 cm(2) of electrode surface, the resistance increases from 7 12 to about 200 12 during the first hour of work, than it decreases down to 2 Omega in 350 h. In this condition, high values of heterogeneous electron-transfer rate constants for ferro/ferricyanide are measured in the order of 10(-4) cm/s, indicating a semi-metallic behaviour of the samples. Results from Raman analyses are also presented and a possible explanation of the observed behaviour of the samples is proposed, in terms of both the intrinsic movement of the H within the structure of the film and the variation of free acceptor levels associated to the B atoms in the lattice. (c) 2006 Elsevier B.V. All rights reserved.