As a result of the theoretical analysis of the dynamics of the membrane method for estimating effective diffusion coefficients in porous pellets relations have been established between moments of the response curves and the parameters characterizing the process considered. The main aim of this analysis was to determine the influence of the mixing phenomena in both chambers, in which the streams are contacted with the faces of porous pellets, on the values of moments of the response curves. A range of experimental parameters has been defined, over which the additivity rule of moments is valid. Carrying out experiments in this range facilitates considerably the estimation of effective diffusion coefficients.