A model for isothermal bound water diffusion in grains and other starchy materials was derived. Assuming that spreading pressure gradient is the driving force for diffusion, an analytical expression for the variation of diffusion coefficient with moisture content was derived. When applied to predict the variation of the diffusion coefficient with moisture for some cereal grains and starches, the curves show a maximum for moisture contents about 0.10-0.15 kg water per kg dry solid. The expression for moisture variation of the diffusion coefficient was used to simulate the drying behavior of cereal grains for known values of initial and equilibrium moisture contents with satisfactory results. (C) 2003 Published by Elsevier Ltd.