The recognition of macromolecule abnormalities in various metabolic or immunologic related disease states has led to the use of plasma exchange for therapeutics. Limitations of plasma exchange, however, exist. Membrane plasma filtration provides a practical alternative. Solute removal can be made selective by the choice of operating conditions as temperature and the selection of the membrane/module design. The optimal temperature range is a function of the plasma type, solute concentrations and membrane system. Operation at below physiologic temperature (cryofiltration) is particularly suited for the removal of cold aggregative solutes, while operation at near or above physiologic temperature is more suited for the separation of solutes having large size differences at normal physiologic temperature. Membrane filtration is simple and safe to perform, is more selective than plasma exchange, does not require plasma product infusion and is more versatile than selective sorption in its applications.