In this study, the diffusion characteristics of theophylline through polyurethane (PU), polyvinylchloride (PVC) and polyhydroxyethylmethacrylate (PHEMA) membranes were investigated for their usage as oral controlled-release reservoir systems. PU and PVC membranes were prepared by the solvent-casting method and PHEMA membrane was prepared by bulk polymerization of 2-hydroxyethylmethacrylate in different thicknesses. Diffusion measurements were performed in simulated gastric fluid and simulated intestinal fluid during 10 h at 37-degrees-C using a diffusion cell. Permeability coefficients calculated from diffusion experiments were found to be approximately 10 times higher in PHEMA and PU and PVC membranes.