The thermal decay of the cation radical of tetramethylbenzidine (TMB) with aqueous nucleophiles was examined in positive (benzyldimethylhexadecylammonium chloride, BHDC) and negative (sodium bis(2-ethylhexyl) sulfosuccinate, AOT) reverse micelles. It was shown that the rate constants are slightly affected by the sign of the interfacial charges, contrary to the situation that prevails in direct micelles. A correlation between the dependence of the decay rate constant and the density of the surfactant molecules on the water pool size has been established in the range 5 less than or equal to omega degrees less than or equal to 25 for all the micellar solutions. This result points out the decisive role of the bound water of the interfacial region, when the electron transfer occurs from the aqueous to the lipidic phase.