The effect of sample size on the characteristic Case 11 solvent front penetration behavior has been investigated in a methanol-PMMA bead system at 25 degrees C in the particle diameter range of 0.125-1.280 mm. The observed induction time generally increases, whereas the front penetration rate exhibits a weak decreasing trend, with increasing sample diameter. Such dependencies of induction time and front penetration rate on sample size, although not predicted by existing theories of Case 11 diffusion, can be attributed to the size-dependent nature of several physical processes originated from the Fickian precursor penetrating ahead of the moving solvent front in an inhomogeneous swelling system of finite dimension. (c) 2006 Elsevier Ltd. All rights reserved.