Sulfonated polyethylene membranes have been obtained by reacting flat sheets of commercial polyethylene with a gaseous mixture of chlorine and sulfur dioxide with subsequent hydrolysis of the sulfonyl chloride groups. Polyethylene materials with various densities have been utilized. Depending on the polyethylene density and on the operating conditions of the chlorosulfo- nation reaction, membranes with various contents of acidic sulfonate groups have been produced. These membranes have been characterized for the ion-conduction and also for the permeation properties of methanol molecules at various temperatures between 25 and 60 °C. Some of these membranes showed hydrogen ion conductivity near 1 10ÿ1 Xÿ1 cmÿ1 at room temperature.