Mint (Mentha viridis), verbena (Lippia citriodora) and sage (Salvia officinalis) are the most produced and consumed aromatic herbs in Morocco. The sorption isotherms of the three plants were determined within the range of 10-90% relative air humidity at three different temperatures (25 degreesC, 40 degreesC and 50 degreesC), using saturated salt solutions method. Henderson's equation was fitted to the experimental data and the agreement between experimental and calculated values was satisfactory. The comparison between the sorption isotherms of mint, verbena and sage is studied. (C) 2000 Elsevier Science Ltd. All rights reserved.