Abstract: An improvement is provided in a process for the membrane filtration of a protein solution. The improvement consists of applying a high shear force at the surface of the membrane. In embodiments of such process, the liquid is subjected to membrane filtration utilizing a rotating membrane disc mounted in close proximity e.g., about 1/8" to about 1/4" to a stationary solid disc, or a rotating solid disc mounted in close proximity e.g., about 1/8" to about 1/4" to a stationary membrane surface with the relative rotation being between bout 1,000 and about 3,450 RPM. This results in permeation characteristics of the selected membrane which essentially represents its theoretical molecular weight cut-off.