Plasma separation using membranes is equally as effective as plasmapheresis using a cell separator. 2. In Goodpasture's syndrome pulmonary haemorrhage improves very quickly with plasma separation. In patients with multiple myeloma, hyperproteinaemia is easy to correct. 3. Plasma separation is well tolerated, both subjectively by the patient and objectively by the circulation. 4. Since the membranes are permeable not only to IgG but also to IgM, circulating antigen-antibody-complement complexes must also be easy to remove using the plasma separation method.