A new kinetics model, a combined second-order-diffusional kinetics model, was developed and compared with a pseudo first-order model for the aqueous extraction of total water soluble solids (WSS) from yerba mate leaves. The model that coupled two mechanisms fits the experimental data more satisfactorily (E% = 1.2 to 2.2) than the pseudo first-order model (E% = 3.9 to 4.4). The second-order-diffusional model could explain the first seconds of the WSS extraction and how the different mechanisms contributed to the concentration of the extract. Temperature influenced the kinetics parameters, but the equilibrium concentrations and the extraction yield were not significantly influenced in a temperature range between 40 and 70 degrees C. (C) 2009 Elsevier Ltd. All rights reserved.