Abstract: The method of treatment called peritoneal membrane plasmapheresis for removal of plasma proteins is enhanced by specification of a sequence of two or three solutions for instilling into and draining from the peritoneal cavity. Solution 1 contains a vosodilator, solution 3 contains no vasoactive drug, and solution 2 contains a vasoconstrictor. Choice of the sequence of solutions to be instilled and drained according to the claimed methods results in sustained opening of peritoneal membrane pores and substantially elevated rates of plasma protein removal, avoiding the problem of declining rates due to local tissue compensatory mechanisms which are observed when only solution 1 is used. Resulting protein removal rates in an anticoagulated patient compare favorably with those attainable with extracorporeal phasmapheresis. An analogous process may be carried out to increase the pore size of any biological membrane accessible to the solutions.