Transient response curves are obtained by perturbing the steady-state concentration of the input stream to a "gradient-free" sorption vessel. The response curves are interpreted by means of a mathematical model to give values of the slope of the sorption isotherm and the effective diffusivity. The method was evaluated using the system: zeolite NaX-propylene-nitrogen. The assumptions of the mathematical model are well supported except for the assumption of negligible truncation error in the values of the sorption parameter. The sorption isotherms and heats of sorption agree reasonably well with other results where comparisons can be made. The concentration dependence of the effective diffusivity is explained by the mathematical model and the nonlinearity of the sorption isotherm.