Formation of dye-induced mixed premicellar aggregates from binary surfactant solutions is proposed for the determination of alkyltrimethylammonium surfactants at the muM level. The Coomassie Brilliant Blue G (CBBG) dye, negatively charged, induces the formation of cationic surfactant aggregates at concentrations far below the cmc. The role of CBBG in the formation of premicelles was studied by using pyrene as a fluorimetric probe. Formation of CBBG-cationic surfactant aggregates of well-defined stoichiometries that depend on the total surfactant concentration added is demonstrated. Also, the influence of analytical parameters affecting the concentration at which a given aggregate is formed was studied. Linear calibrations for alkyltrimethylammonium surfactants were obtained by using different cationic surfactants as titrants; therefore, the previously derived measurement parameter for mixed micelles is applicable to premicellar aggregates as well.