It has been shown by Hipp, Groves, Custer & McMeekin (1952) that the differential solubility in urea of the casein components of cow's milk can be utilized for preparative purposes. Fractionation is achieved by step-wise dilution of a solution of all the casein components in strong (6·6 molar) urea. In connexion with the work on the three genetically distinct β-caseins discussed in the preceding paper, the need arose to prepare the variants A, B and C from the milk of appropriate homozygotes. This led to the development of the modified procedure described in this note, a procedure more sparing in urea and more effective in the initial isolation of the β-casein fraction than the original method of Hipp et al.