AbstractThis paper presents results based on concentration quenching of fluorescence polarization (cqfp), which demonstrate the feasibility of using cqfp to measure changes in hydrogel‐membrane hydration. This is accomplished by binding fluorescent molecules to the hydrogel matrix, and showing that the fluorescence polarization is a monotonic function of fluorophore concentration. Films based on crosslinked 2‐hydroxyethyl methacrylate containing lissamine side groups (10−4‐10−7 mol/l) were mounted in a special cell which provided an aqueous environment, and in which polarized fluorescence could be measured. An argon‐ion laser provided polarized excitation at 488nm, and the polarized fluorescent emission was detected. The correlation between the fluorescence polarization and the bound dye concentration was found to correspond to the theoretically expected behavior.