Membranes derived from the polyelectrolyte complexes of polyvinyl ether of monoethanol amine and poly-N-methyl-4-vinylethynyl piperidinol-4 with polyacrylic acid and copolymers of acrylic acid and vinylbutyl ether have been prepared and their swelling properties were studied as a function of copolymer composition, solvent composition, pH, ionic strength and temperature. The permeability of polyelectrolyte complex membranes with respect to urea has been also considered. (C) 2001 Elsevier Science Ltd. All rights reserved.