The esterification of lactic acid with ethanol and the hydrolysis of the corresponding ester, ethyl lactate, have been studied in the presence of the commercial cation-exchange resin Amberlyst 15. The influence of different operating parameters such as stirrer speed, catalyst particle size, initial reactant molar ratio, reaction temperature and catalyst loading, has been examined. Additionally, the adsorption constants for the four components on Amberlyst 15 were determined by performing adsorption experiments between two non-reacting species. The values found for the adsorption constants follow the order: water > ethanol > lactic acid > ethyl lactate. Experimental kinetic data of the esterification and the hydrolysis reactions were correlated simultaneously with the Langmuir-Hinshelwood (LH) and pseudo-homogeneous (PH) models. The activity coefficients were calculated according to the UNIQUAC model. The LH model gave the best agreement with the kinetic experimental data. The activation energy of esterification and hydrolysis reactions were found to be 52.29 and 56.05 kJ mol(-1), respectively. (c) 2006 Elsevier B.V. All rights reserved.