In this study a new method for the separation of casemomacropeptide (CMP) from native whey proteins has been developed. This new method includes the pretreatment of whey protein concentrate with the enzyme transglutaminase followed by microfiltration. The amino acid sequence of CMP includes two glutamine and three lysine residuals, whereby this peptide can be crosslinked by tranglutaminase, whereas the native whey proteins show much less sensitivity to be crosslinked by this enzyme due to their globular structure. The covalent linked CMP aggregates can be removed be means of microfiltration or diafiltration. The results show that this technique can be successfully used to obtain a CMP-free whey protein concentrate from sweet whey, which can be further used for the fractionation of individual whey proteins after CMP removal. (C) 2004 Elsevier Ltd. All rights reserved.