Solute transport through interpenetrating polymeric networks of poly(vinyl alcohol) and poly(acrylic acid) at pH 3 or 6 was studied in order to investigate the influence of possible solute binding on the transport process through the networks. Diffusion of theophylline, vitamin B-12, and myoglobin was analyzed, and diffusion and partition coefficients were determined. Analysis using the free volume-based theory of Peppas and Reinhart indicated that solute binding occurred only in those hydrogels that were in the ionized state. ATR-FTIR spectroscopic studies were used to determine the level of binding in the case of myoglobin in contact with these IPN hydrogels.