Available approximate expressions used in the kinetic data treatment of (scanning electrochemical microscopy) SECM experiments in the case of steady-state feedback currents with irreversible reaction at the substrate and a microdisk tip arc discussed. The necessity of new expressions is thus pointed out. A new expression of the current is then produced and discussed. It covers all usual experimental configurations (microdisks with R-g below 20, R-g characterizing the surrounding insulator thickness) and dimensionless tip-substrate distances larger than 0.1, with an accuracy of +/- 0.025 for any kinetics. (c) 2007 Elsevier B.V. All rights reserved.