A kinetic study of the reaction between [Fe(CN)(6)](4-) (hexacyanoferrate (II)) and [Co(en)(2)Cl-2](+) (traits-dichlorobis cobalt(III) bis(ethylenediammine)) has been carried out in sodium dodecyl sulphate (SDS) micellar solutions containing NaCl. The results are discussed by using an approach based on the pseudophase model. Trends in the observed reactivity are explained by a change in the degree of association of one of the reactants ([Co(en)(2)Cl](+) in the present Letter) to the micelles, which depends on the surface potential of the micelles. The electrostatic and non-electrostatic components of the free energy of binding are determined by two different methods and the results of these determinations are compared. (c) 2005 Elsevier B.V. All rights reserved.