We are currently investigating the interactions of chitosan-heparin polyelectrolyte multilayers (PEM) with model proteins (bovine serum albumin, chicken egg white lysozyme, and myoglobin). Heparin and chitosan are naturally derived polysaccharides with biochemical function that makes them interesting potential materials for tissue engineering. They also behave as polyelectrolytes. We are interested in the potential ability of chitosan-heparin PEM and to bind and stabilize proteins for tissue engineering applications. PEM can be prepared with terminal layers exhibiting positive, negative, or neutral charges. The quantity and stability of bound proteins were investigated by polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) combined with hydrogen deuterium exchange experiments. The secondary structure of the adsorbed proteins was investigated by studying the amide I peak region in the IR spectra from the PM-IRRAS, and by evaluating the degree to which protons can be exchanged for deuterons. The secondary structure of the adsorbed protein was compared to its structure in solution obtained via Fourier transform infrared spectroscopy (FT-IR). Both native and heat-denatured proteins were studied in solution. PM-IRRAS is shown to be a useful technique for investigating the stability of surface-adsorbed proteins with respect to different potential mechanisms of protein degradation (e.g. hydrolysis, aggregation, unfolding), on biomedically relevant surface coatings exhibiting different surface charges.