In this research, the most commonly used equilibrium moisture content (EMC) and equilibrium relative humidity (ERH) equations are compared on their ability to best fit the published sorption data for selected medicinal and aromatic plants. A non-linear regression technique is used to fit data subsets. In order to compare the performance of the EMC/ERH equations, three statistical error parameters are used. The best-fitted equations which provide a sound basis for future work on drying and storage of medicinal and aromatic plants are given. (C) 1999 Silsoe Research Institute.