Caseins are phosphoproteins kept together by non-covalent interactions to form a highly stabilised dispersion in milk. This study intended to evaluate the different effects of denaturing solvents and solutions on caseins in order to optimise the chromatographic resolution for a better identification of individual casein fractions. The caseins were obtained from bovine skimmed milks by precipitation at pH 4.3, and the proteins were dissolved in water and three different solutions. The casein separation was performed by reversed-phase high-performance liquid chromatography. Each casein was identified by matrix-assisted laser desorption ionisation-time-of-flight mass spectrometry. The best result was achieved by treating the caseins with solution D.