A set of methods (D-1-D-8 transient sorption and permeation analysis system) previously used for the regular inhomogeneous membranes, that is, the membranes where the diffusive properties vary regularly along the diffusion axis, has been applied to the concentration-dependent diffusion in order to deliver experimental protocols to recover the notion of the diffusion coefficient. On the basis of the numerical studies of c(t) = (D(c)c(x))(x) for carefully chosen set of D(c) functions, the "diagnostic system" has been created. It provides a possibility of a realistic estimation of the D(c) relationship as well as the reasons for the deviations of the transient measurements from the ideal Fickian behavior.