Poly(2-hydroxyethyl methacrylate) membranes were prepared in aqueous media with different ions and ionic strengths. The enzyme glucose oxidase was incorporated into some of these membranes. It was found that membrane water contents and ionic strengths have a linear relationship as long as the salt is not changed. When the salt was varied, only a relationship between salt concentration and water content could be observed. The membrane permeabilities were all found to be of the same order (10(-8) cm2 s-1) but the membranes were slightly more permeable to chromate ions than glucose. Incorporation of enzyme distinctly increased the water content of the membrane and permeability to both solutes.