Ultrafiltration membranes are used by the biopharmaceutical industry for protein concentration, and buffer exchange. Increasingly rapid process development efforts call for filtrations devices to provide simple linear scaling from the bench, to pilot and production scales. However, the flux and retention performance of UF membranes are heavily influenced by concentration polarization. In order to provide reliable data, scaling tools must generate hydrodynamic conditions equivalent to the process scale. Essential design elements for effective scale down tools will be discussed, as well as the influence of filtration control scheme on scaling. Mass transfer based models will provide a robust method of scale up.