This study determined the diffusion coefficient during hot air drying of mushrooms (Agaricus blazei). Experimental drying kinetics were applied to sliced mushroom at different air temperatures (45, 60, 75, and 80 degrees C) and air velocities (1, 1.2, 1.75, 2.3, and 2.5 m/s) in order to find an analytical solution to the mass transfer equation for drying using an inverse problem with two distinct optimization techniques: Levenberg-Marquardt and Differential Evolution, in successive trials. The experimental data were also modified by a normal distribution random error. Statistical analyses showed no significant differences between reported and estimated curves. The diffusion coefficients are greater in mushrooms dried at higher temperatures, and those dried at higher drying air velocities. (C) 2009 Elsevier Ltd. All rights reserved.