Two methods are developed for the determination of the diffusion parameters of a penetrant inside polymer membranes whose diffusivity varies exponentially with its concentration. Two cases are considered in this report depending on the sign of the plasticization coefficient parameter. The method using differential permeation data is based on the correlations between the slope of the reduced permeation flux versus time plot at the inflexion point, and the two key parameters of the concentration-dependent diffusivity laws. For the transient sorption/desorption method, the slope of the penetrant mass uptake versus square-root of time curve leads to the same parameters of the diffusion law via similar correlations. No specific computer software is required for the use of these methods and they are user friendly. (C) 2009 Elsevier B.V. All rights reserved.