The swelling capacity and release rate of two homologous drugs, theophylline and aminophylline, from acrylic acid/n-alkyl methacrylate hydrogels have been studied. The maximum equilibrium swelling increases as the molar fraction of acrylic acid or the chain length of the methacrylate in the hydrogels increases. Water diffusion to the hydrogels is non-Fickian. Both drugs are released from the fully swollen hydrogels according to Fick's law. However, the. drug release from xerogels deviates from Fick's law, especially for aminophylline. As expected because of its larger size, aminophylline diffuses more slowly than theophylline under similar experimental conditions. (C) 2004 Wiley Periodicals, Inc.