A series of novel hydrogels were prepared from acrylic acid (AA), N-vinyl pyrrolidone (NVP), and chitosan by photopolymerization. The swelling behaviour, gel strength, and drug release behavior of the poly(AA/NVP) copolymeric hydrogels and corresponding interpenetrating polymer network hydrogels were investigated. Results showed that the swelling ratios for the present hydrogels decreased with an increase of NVP content in the gel, but the gel strength increased with an increase of NVP content in the gel. Results also showed that the drug-release behaviour for the gels is related to the ionicity of drug and the swelling ratio of the gel. (C) 2003 Wiley Periodicals, Inc.