Potentials for the one-electron reduction of nine 5-substituted N-methylisatins were measured in ten aprotic solvents by cyclic voltammetry. Best-fit Hammett sigma substituent constants were determined and used in Hammett plots to determine reaction constants, rho, for all solvents. Correlations of solvent polarity parameters with the Hammett rho values and with measured reduction potentials suggest that empirical solvent parameters that reflect the strength of solvent molecular cohesive forces and solvent Lewis acidity are important predictors of the ability of solvent to facilitate the one-electron reduction of isatins in aprotic media by stabilizing the radical anion reduction products. (C) 2010 Elsevier B.V. All rights reserved.