A new method to determine adsorption isotherms is suggested. The method is based on analysis of the nonlinear frequency response of a chromatographic column. Due to the fact that higher order frequency response functions (FRTs) are included in the analysis, the method is in particular useful to determine isotherms with more complex shapes, e.g., isotherms possessing inflection points. By theoretical derivation of the first-, second-, and third-order FRFs and their analysis, it is shown that the first, second, and third derivatives of the corresponding adsorption isotherm can be estimated from the low frequency asymptotes. The analysis presented is made for the adsorption of a single component. The description of the chromatographic column is based on the equilibrium-dispersion model. The extension of the method considering the possibility of a finite mass transfer rate in the column is also presented.