This work introduces a new method for tracer diffusion studies which emphasizes interfacial effects. Total internal reflectance fluorescence (TIRF) was employed to monitor rhodamine dye tracer diffusion normal to the interface in PDMS films whose swelling in THF was constrained by adhesion to a rigid support. In these constrained films, the tracer diffusivities were equal to or lower than those in freely swollen samples, with the difference most pronounced in samples of relatively low crosslink density. This indicated that swelling was reduced by adhesion to the substrate. In the supported films, tracer diffusion deviated from Fickian kinetics, suggesting that the region of the film near the substrate contained relatively less solvent at equilibrium than did the bulk film.