High-sensitivity differential scanning calorimetry was applied for the first time to study the micellization of bovine beta-casein in aqueous solutions, complemented by analytical ultracentrifugation data. The micellization was described as a single endothermic heat capacity peak located in the temperature range of 0-50degreesC. The transition originated at temperatures very close to 0 degreesC. The position of the heat capacity peak was strongly dependent on the protein concentration and the solvent composition. Thermodynamic parameters of the micellization, the transition temperature and enthalpy, were determined over a wide range of protein concentration. The observed thermal behavior of beta-casein was well fitted by the thermodynamic shell model of micellization proposed by Kegeles (J. Phys. Chem. 1979, 83, 1728). The effects of different cosolutes (inorganic salts, urea, Tris, and ethanol) on the thermodynamic parameters of micellization of beta-casein underline the hydrophobic character of the transition.