A mathematical approach based on the combined application of Fick's law of diffusion and the Beer-Lambert law was used to measure the diffusion coefficient of dyes viz., coumarin 515 [3-(1-methylbenzimidazol-2-yl)-7-diethylaminocoumarin], POPOP [1,4-bis (5-phenyloxazolyl-2-yl) benzene], and exalite 416 {1,1, 1',1'-tetra ethyl -5,5'-diparaanisyl-[2,3:5,6] diindanobenzene} in solutions of polystyrene and poly(methyl methacrylate) in 1,4-dioxane. Diffusion data agreed well with the published results obtained using other techniques. (C) 2004 Wiley Periodicals, Inc.