The process of geometrical modification of pores in poly(ethylene terephthalate) track-etched membranes (TM) by use of plasma deposition of a fluorine-containing polymer protective layer on one membrane surface and alkali etching of the other surface has been studied in order to produce membranes with improved performance characteristics. Samples of membranes with conical pores have been obtained which have better filtration efficiency compared with initial TM with cylindric pores. Plasma polymerization of IH,1H,2H-perfluoro-1-octene at the membrane surface was used to produce the protective layer resistant to alkali solutions. The occurrence of plasma modification and changing of pore geometry have been verified by X-ray photoelectron spectroscopy and scanning electron microscopy studies. The filtration efficiency and selectivity of the modified membranes have been studied. (c) 2008 Elsevier B.V. All rights reserved.