For the purpose of determining the quantity of dyes sorbed in monomolecular and aggregate state in the substrate, the sorption isotherm for Congo Red on cellophane film was determined at 97$^{circ}C$ in absence of salt. A modification of existing sorption isotherm was attempted through discussion of the fading behavior of Congo Red sorbed only monomolecularly in the substrate. The data showed considerable correlation much more with the proposed sorption isotherm than with the generally used one. (Received Feb. 28, 1973)