Solubilization of polycyclic aromatic compounds in aqueous di lute solutions of three cationic amphiphiles was studied. The maximum additive concentrations (MACs) of the aromatic compounds were constant below their critical micelle concentrations (cmcs) and monotonically increased above the cmcs. The first stepwise association constants ((K) over bar)(1) between a solubilizate monomer and a vacant micelle were evaluated from the MACs for the solubilizates using the mass action model for solubilization into micelles in the dilute solution. The standard Gibbs energy changes of solubilization (DeltaG degrees) were calculated from (K) over bar (1), and the enthalpy and entropy changes of solubilization were estimated from the temperature dependence. MACs of each surfactant at the same surfactant concentration above the cmc were different depending on the cmc, but there was little difference in the DeltaG degrees values. Some differences appeared in the enthalpy and entropy values in accordance with their micellar size or degrees of counterion binding to micelles. DeltaG degrees for solubilization decreased linearly with carbon number of aromatic solubilizate for each micellar solution.