Whey is a liquid by-product of the dairy industry produced during the manufacture of cheeses and casein. As a raw material, it has many applications in food technology due to the functional and nutritional properties of its proteins. Membrane technology, especially ultrafiltration (UF), has been used in the dairy industry to produce whey-protein concentrates, because this technology allows the selective concentration of the proteins in relation to the other components. In this context, the objective of this work was to concentrate and to purify the whey proteins using UF in association with discontinuous diafiltration (OF). The two strategies were tested by changing the volumetric-concentration factor (VCF), the OF water volume and the number of DF steps. The results showed that the UF process is adequate for the production of protein concentrates; in the best experimental strategy, the protein concentrate obtained was greater than 70% by weight (dry basis). (C) 2011 Elsevier B.V. All rights reserved.