The solubilization of amphiphilic hemicyanine dyes by the micelles of a cationic surfactant? cetyltrimethylammonium bromide (CTAB), was studied as a function of surfactant concentration above the critical micelle concentration(CMC). The micelle-water partition coefficient, K-x, and the standard free energy of solubilization, Delta G(0), of these dyes in CTAB micelles was determined at 25.0 degrees C by a differential spectroscopic method. The CMCs of CTAB in the presence of small amounts of these dyes were determined by a conductivity method at 25.0 degrees C. The values of K-x and Delta G(0) for all six dyes were determined by an improved method that incorporates both conductance and differential absorbance data.