Cationic alkylpyridinium halide surfactants have been used as quenchers of pyrene fluorescence in polyelectrolyte-surfactant systems such as sodium polyacrylate-alkyltrimethylammonium halide. We use ideal mixing theory to demonstrate that for quencher molecules more strongly bound than the surfactant, the mole fraction of quencher in the micelles may be significantly greater than the mole fraction in the bulk. mixture. As well, the mixed surfactant system has a lower critical aggregation concentration and a higher degree of binding than the pure surfactant system. These effects should be considered both when planning experiments and when calculating aggregation numbers. In cases of significant perturbations, the use of pyrene excimer quenching or neutral quenchers may be preferable.