Concentration of milk and whey by ultrafiltration and reverse osmosis (RO) in cascade mode is an amendment of evaporation for high volume reduction ratios (VRR) prior to drying. This study investigated the impact of a prior protein removal and the transmembrane pressure (TMP) on the RO stage, compared to skim milk and sweet whey. It could be found that removal of the protein fraction of both skim milk and sweet whey improved the efficiency of the RO. An upstream ultrafiltration resulted in higher VRR as well as an increased permeate flux.