A numerical approach to determining the secondary current-density distribution in a new class of microelectrochemical sensors with critical dimensions in the range 20-50 mum high by 100-500 mum wide and 1-10 cm long is described. The finite element method is employed to solve the relevant fluid dynamic, mass transport, and potential distribution equations in three dimensions to reveal quantitative information on the current-voltage response. The Tafel slope of the device is calculated for a range of electrolyte conductivities from 0.001 to 0.01 Omega(1-)cm(-1), and the distortion in the current-voltage curves from working with low conductivity solutions is determined. The effect on the current-voltage curve of using a range of reference electrode positions is investigated, and the optimal configuration is discovered. Finally, the current-voltage response of a multi-working electrode device is calculated using a finite element simulation for a cell of dimensions 400 mum high and assumed infinite width, for a range of offset potentials.