The TTAB-butanol system has been studied over a temperature range of 15 to 35 degreesC and at butanol concentrations up to 0.3 mol/kg. The CMC vs temperature curves have a smooth minimum whose location is not markedly influenced by alcohol presence. The molar fraction of butanol in the micelles and the entropy of micellization have been calculated using a theoretical treatment of critical micelle concentration data based on excess thermodynamic quantities. The heat capacity of micellization has been obtained and compared with results predicted by a recent thermodynamical theory which describes a universal behavior exhibited by ionic surfactants. Both the entropy and the enthalpy of micellization increase with alcohol concentration. The butanol molar fraction in micelles enables us to estimate the standard free energy of solubilization, which is found to decrease with temperature. It is important to emphasize the chance of predicting the value of these interesting thermodynamic quantities without the need for measuring them. The degree of micelle ionization has also been evaluated using two different methods, and no significant differences have been observed. Copyright 1997 Academic Press.