Dialkyl viologens are known to be effective catalysts in the oxidation of carbohydrates under alkaline conditions and are being investigated for use in direct-carbohydrate fuel cells (DCFCs). However, dialkyl viologens hydrolyze to more stable monoalkyl viologens under alkaline conditions. It has been reported that monoalkyl viologens also act as catalysts for the oxidation of carbohydrates, but little was known about the electrochemistry of monoalkyl viologens. Other researchers have investigated the redox dyes indigo carmine and methylene blue for use in DCFCs. In the present report monoalkyl, aminoalkyl, and dialkyl viologens, as well as indigo carmine and methylene blue, were examined using the method of cyclic voltammetry. These species were tested in acetonitrile, dimethyl sulfoxide, and water. Redox potentials, diffusion coefficients, and heterogeneous electron-transfer rate constants are all reported. Stability in alkaline solution and aqueous solubility are also examined in a semi-quantitative fashion. A comparison between viologens and the other redox dyes is made and recommendations are given on the use of viologens as catalysts. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.006211jes] All rights reserved.