The separation of cows', sheep's and goats' milk casein components by HPLC on a strong anion-exchange (P.L-SAX 8 mu 1000A) column is described. During HLPC, whole caseins of the three kinds of milk behaved differently from conventional separations. The casein components of the three kinds of milk were well resolved under the chromatographic conditions used. HPLC resolved the kappa-caseins better than did ion-exchange chromatography on DEAE cellulose, and was particularly efficient in the case of goats' milk. Goats' and sheep's milks had almost similar chromatographic profiles but these differed considerably from that of cows' milk. Caseins from the sheep and the goat were also similar in that a shallower NaCl gradient was required for the separation of casein components than for cows' milk.