In moving protein purification processes from the bench to production scale, the focus must shift increasingly to practical issues related to economics. More rapid and efficient bioseparation processes that operate at low pressure provide savings in both capital and operating costs. Also, faster protein product isolation early in the purification process can improve product yield and cost-effectiveness by limiting proteolysis and denaturation. Toward these processing goals, significant advances have been made in analytical to preparative level column chromatogra­ phy through the use of more size-monodisperse and smaller packings which mini­ mize dispersion and reduce diffusion times to interior binding sites within gel particles. However, as column methods are scaled, constant performance typi­ cally comes at an increasingly alarming cost due to the high price of monodisperse, small bead packings, and the high pressure drop across even shallow beds of these particles [1-3]. Alternatives to standard packings and column geometries have been proposed and marketed in recent years including perfusion chromatog­ raphy [4] and membrane chromatography [5-7] which hold promise for improved scalability and economic viability.