The pattern of conductivity and electrochemical activity at the surfaces of hydrogen-terminated boron-doped diamond electrodes, with different boron doping levels, were measured using conductive probe atomic force microscopy (CP-AFM) and scanning electrochemical microscopy (SECM). CP-AFM showed that the surface was predominantly insulating, with discrete conducting areas of less than 2 mum in diameter, randomly and nonuniformly distributed on the surface. SECM imaging correlated these conductive areas with electrochemical activity and showed that the electrode surface was only partly electrochemically active and that the active area of the electrodes increased with boron doping level. Cyclic voltammograms and SECM approach curves obtained using Ru(NH3)(6)(3+/2+) as the redox mediator were characteristic of those obtained at partially blocked electrodes of nonuniform activity, or a microelectrode array. By use of this model, the SECM approach curves could be fit to obtain values of the fraction of the surface that was electrochemically active. The active area of the electrode was related to the boron doping level.