The results of a series of scratch measurements are reported for a number of methyl alcohol (methanol) plasticized poly(methylmethacrylate) (PMMA) surfaces to investigate the deformation mechanism and solvent diffusion characteristics when a PMMA is exposed, to various extents, in a methanol environment. The study confirms that the solvent diffusion in this system occurs by the Case II diffusion process. The scratch deformation map described indicates that there is a major change in the deformation mechanism as the exposure time proceeds and this is related first to a sample plasticization and then to a restructuring process of the PMMA-methanol system due to the greater mobility and relaxation of the polymer molecules as they imbibe the solvent.