Analytical approximations for steady-state negative feedback currents in scanning electrochemical microscopy (SECM) experiments using a microdisk are discussed. Previously published results are precisely discussed and lead to an analytical approximation valid (with an error below 0.01 on normalized current) for all values of tip-substrate distances and microdisk with an insulator thickness characterized by R-g values between 57 and 1000. More interesting from an experimental point of view, the use of new mathematical expressions allows the proposition of an analytical expression valid for all values of tip-substrate distances and microdisk with Rg values between 1.3 and 62. (c) 2007 Elsevier B.V. All rights reserved.