This paper demonstrates the feasibility of using cascade ultrafiltration systems run at constant flux for efficient purification of lysozyme from chicken egg white. Integration of high-resolution purification with concentration is a key requirement in the purification of lysozyme, which is present at very low purity and concentration in egg white. A three-stage cascade ultrafiltration system, which focused on purification alone, gave a continuous diluted lysozyme product stream of 96% purity with over 75% recovery. Process variables such as the retentate to feed ratio as well as internal recycle rates within the cascade were found to have significant effects on the efficiency of separation. These findings could be explained using a material balance based mathematical model. A four-stage cascade system which integrated both purification and concentration attributes produced a continuous, 97% pure lysozyme product stream with over 71% recovery and with an almost twofold lysozyme concentration enrichment. This system, which utilized a high degree of buffer recycling, is likely to be attractive for economic large-scale protein purifications in general. (C) 2009 Elsevier B.V. All rights reserved.