A mathematical model to predict the drying kinetics of shrinking bodies was proposed, assuming unidirectional drying and three-dimensional shrinkage. The differential equation for mass transfer in a finite slab was solved, using boundary conditions of the first kind. The model was numerically solved by finite differences, taking into account a convective term in the mass balance equation, which appears as a consequence of non-unidirectional shrinkage. This additional term significantly changed the value of the predicted diffusion coefficient. Differences when compared with previous solutions are significant for drying of solids with high initial moisture content. Numerical solutions were obtained for absorption as well as for desorption processes. The predicted apparent diffusion coefficients, calculated from the slopes of the semilog drying kinetics curves, were different in both cases. (C) 2002 Elsevier Science Ltd. All rights reserved.