In their article, ‘‘AC frequency characteristics of coplanar impedance sensors as design parameters’’, Hong et al.1 present an analytical model for the calculation of the resistance between two electrodes in a microchannel. However, their measurements fit poorly with their suggested model, and they attribute the discrepancies to electrode thickness and a ‘fringing effect’. In this note we show that the discrepancies are due to the neglected channel height in their model, and that by including two additional transforma ions, the resistance between two