The transport of buffer solutions (pH 4.1-7.2) in hydroxyethyl methacrylate copolymer (HEMA) is investigated. The diffusion coefficient of Case I transport, the velocity of Case II transport and the activation energy of the transport process in non-irradiated HEMA are determined. The buffer transport in HEMA copolymers irradiated by gamma -rays in vacuum and in air is also studied. After irradiation, the data of mass gain at the short times and long times are designated as stages 1 and 2, respectively. The first stage is followed in Case I transport when the specimen is irradiated in vacuum and the anomalous transport when irradiated in air. The second stage, regardless of the irradiation atmosphere is followed in Case II transport. The equilibrium swelling ratio of irradiated specimens increases significantly when the pH value is greater than 5. A volume transition is observed at high gamma -ray doses. The effect of gamma -ray irradiation on the functional groups in the polymer is investigated using the infrared spectra. (C) 2001 Elsevier Science Ltd. All rights reserved.