The use of supercritical fluid and specifically carbon dioxide as carrier to infiltrate various matrices is gaining importance. This study focuses on the impregnation of poly(methyl methacrylate) by a model drug, o-hydroxybenzoic acid (o-HBA), using supercritical carbon dioxide (SCCO2) as carrier and swelling agent, with special emphasis to equilibrium data. A stirred batch reactor equipped with sampling device was employed in order to determine the sorption isotherms with a concentration parameter independent of pressure. The impregnated amount of HBA/g(polymer) was determined at 40 degrees C and 12, 16 and 20 MPa for concentrations of HBA in SCCO2 ranging from 0.05 to 0.7 mg/g. Reproducibility of the impregnated amount was below 3.2%. At the highest investigated concentrations, the uptakes were of 27 mg/g(polymer) when experiments were performed at 12 or 16 MPa, and of 20 mg/gpolymer for the investigations carried at 20 MPa. Experimental data were further correlated by four isotherm types: Langmuir, Freundlich, Sips and Toth. Only the Toth model was found to fit satisfactorily the whole range of concentration, for the three pressures. (c) 2006 Elsevier B.V. All rights reserved.