The isothermal kinetics of the release of the drug (E)-4-(4-metoxyphenyl)-4-oxo-2-butenoic acid (MEPBA) from poly(acrylic acid) hydrogel were studied. The isothermal kinetic curves of MEPBA release from the poly(acrylic acid) hydrogel in bidistilled water at different temperatures ranging from 22 degrees C to 42 degrees C were determined. The reaction rate constants of the investigated process were determined using the initial rate, saturation rate and power law. Also, to quickly determine the kinetic model of drug release, the so-called method of reduced time was applied. The influence of the degree of the MEPBA released (alpha) at the values of the kinetic parameters as well as the presence of a compensation effect was established. The procedure for determining the distribution function of activation energies was developed. This procedure was based on the experimentally determined relationship between the activation energy and the degree of drug released. The process of MEPBA release from PAA hydrogel. almost in entire range. can be described with the model of the drug desorption from the active centers with different specific energies. (C) 2007 Elsevier B.V. All rights reserved.