Accurate analytic expressions are obtained for the chronoamperometric current and the general (quasi-reversible) i-E characteristics of planar inlaid microelectrodes. These expressions involve the area and the perimeter of the electrode and the steady-state diffusion-limited current. The latter can be expressed analytically exactly for circular and elliptic disk electrodes and to an excellent approximation for microelectrodes with any simply connected shape. Our results are tested experimentally for circular disks and for elliptic disks that are produced when a glass-encased carbon fiber is polished at an angle. (c) 2005 Elsevier B.V. All rights reserved.