Rates of the basic hydrolysis of 2-(4-chlorophenoxy)quinoxaline 1 were measured in aqueous cetyltrialkylammonium chlorides, C16H33NR3Cl, R = Me (CTACl), Et (CTEACl), n-Pr (CTPACl), n-Bu (CTBACl). The shape of the rate versus surfactant concentration profiles depends on substrate concentration. At low substrate concentration, first-order rate constants go through maxima with increasing surfactant concentration, but at higher concentration, double-rate maxima are observed. The presence of single- or double-rate maxima is ascribed to reaction in micelles or in premicellar complexes. At low substrate concentration, micellar effects were analyzed by means of a mass-action model. Second-order rate constants k(M), for reactions in the micellar pseudophase increase with headgroup size.