Apparent mass (water and solute) diffusivities were measured during osmotic processing of model fruit (apple) and vegetable (potato) tissues. Among process parameters, temperature had the largest positive effect on moisture (D-w) and soluble solids (D-ss) diffusivity. Increased concentration gave increased mositure and decreased solute diffusivities. The dehydration efficiency index (D-w/D-ss ratio) increased with concentration but measured or remained constant with temperature. Using the right size of osmotic solute it was possible to maintain satisfactory moisture diffusivities with nearly zero net solute uptake. Freeze/thaw-induced tissue damage caused a dramatic decrease in dehydration efficiency. Both moisture and solute diffusivities followed Arrhenius kinetics with activation energies (E(a)) ranging between 21.2 and 29.7 kJ mol(-1) K-1. Cell level explanations on response differences are attempted.