We describe the design, fabrication, and characterization of highly charged polymers with microenvironmental pH properties. Immobilization of a pH-sensitive fluorescent probe in the polymers allows the probe to measure the polymer’s microenvironmental pH. Differences between the external solution and the internal polymer pH values, first observed for immobilized enzymes, highlight the partitioning of hydrogen and hydroxyl ions between the polymer and bulk solution. MAPTAC, possessing a quaternary ammonium group, was used as the positively charged monomer. AAMPS, a sulfonate derivative, was selected as the negatively charged monomer. Ten percent of each monomer was photo-polymerized in poly(HEMA). Fluorescence intensities as a function of external pH changes were recorded both with a microplate fluorometer and a monochromator. Fluorescein, the pH-sensitive probe, exhibited pK(a)s from 3 to 8, depending on the polymer charge.