Magnetic field driven convective transport at inlaid-disk Pt microelectrodes was investigated as a function of the electrode radius (6 less than or equal to a less than or equal to 250 mum) using video imaging and steady-state voltammetry. A uniform magnetic field (B = 1.0 T), oriented orthogonal to the microelectrode surface in order to induce rotational flow, is shown to cause either an increase or decrease in voltammetric limiting currents (- 37 to + 119%) depending solely on the size of the electrode. For inlaid disk electrodes with radii less than similar to 100 mum, the magnetic field driven flow results in a decrease in transport limited current, a consequence of rotational solution flow adjacent to the surface preventing gravity-driven natural convection. The magnetic force at electrodes with radii larger than similar to 100 mum generates a vortex flow pattern, resulting in convective transport of redox reactant from the bulk solution inward towards the electrode surface. The difference in flow patterns is shown to result from a transition from planar to radial diffusion as the electrode size is reduced.