Herein, we report a theoretical study of ring microelectrode scanning electrochemical microscopy approach curves in pure positive and negative feedback modes. The dependence of the simulated approach curves with characteristic dimensions of the ring microelectrode is studied, and accurate analytical approximations are proposed. Moreover, in the specific case of ring micropipet electrodes, the filling level and geometric parameters of the internal void of the pipet affect the transient current distribution. Micropipet design guidelines are therefore suggested that may facilitate quantitative kinetic studies of the underlying substrate. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3374340] All rights reserved.