The release process of a water soluble, model drug (proxyphylline) with small, yet not negligible osmotic action, from silicone rubber (SR) matrices is presented. The kinetics of release for different initial loads of the drug is supplemented by measurements of the kinetics of the concurrent water uptake. To gain insight on the relevant non-Fickian transport mechanisms, the morphology, the diffusion, and sorption properties of the drug-depleted matrices are studied. in addition, both drug-loaded and drug-depleted matrices are characterized with respect to their mechanical properties. The combined information derived from these techniques support-at least below the percolation threshold-the operation of a release mechanism occurring through a uniformly swollen polymer matrix without formation of cracks, in contrast to the release observed in the case of water soluble, inorganic salts where release takes place through a network of microscopic cracks. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 821-830, 2011