A two-phase model for diffusion and drug release through swollen polymeric matrices is presented and solved. This model explains the non-Fickian release behaviour experimentally found for the system constituted by theophylline in a water-swollen scleroglucan matrix in a slab form. The exponential nature of the temporal behaviour of the drug in the stationary phase is confirmed by means of Green function analysis. The boundary conditions deriving from the non-self-sustaining nature of the polymeric gel and from the presence of a net are investigated in detail.