The theoretical model proposed earlier, which assumes that protein molecules in the surface layer can exist in multiple conformations with different molar area, so far has been applied to the equilibrium isotherms of surface pressure, adsorption, and adsorption layer thickness. Here we use the model for the surface dilational modulus, E, measured during area oscillations at given frequencies. Comparing the experimental dependence of the limiting (high-frequency) elasticity, E-0, on the surface pressure for BSA and beta-casein with the theoretical ones calculated for the same set of basic model parameters, we find good agreement between the experiments and the proposed theory. The main factor that affects the dependence of E-0 on the concentration or the surface pressure is the dependence of the mean molar area of protein, omega, on the adsorption, Gamma. The theoretical value of E-0 for proteins is lower than that characteristic for molecules with constant area in the adsorption layer by the factor of (1 + d In omega/d In F). It is shown that for the proteins the derivative d In omega/d In Gamma is negative; for example, for flexible beta-cascin, the value of this derivative approaches -0.9. This value not only produces very low E-0 values but also correctly describes the maximum and minimum values of E-0 measured at fairly low surface pressures.