The dependence of changes in the free energy (−Δ F/ kT) accompanying the adsorption of polystyrenes on the energy of interaction of a polymer segment with the surface of a porous adsorbent (−ε) has been investigated. It is shown that, for macromolecules of any molecular weight (MW) this dependence intersects the −ε axis at the point −ε = −ε cr and, hence, the existence of the critical energy, ε cr, has been verified experimentally. At −ε < −ε cr the probability of entry of macromolecules into the adsorbent pores is determined by the molecular-sieve effect, at −ε > −ε cr the adsorption effect begins to predominate and at −ε = −ε cr these two effects mutually compensate and the separation of macromolecules according to MW (or according to size) does not occur (the distribution coefficient, K d, is unity for macromolecules of any MW). Since the molecular-sieve and the adsorption effects are interrelated, in the range of the molecular-sieve effect, the entry into the pores of macromolecules of higher MW is favoured by adsorption, whereas in the adsorption range the adsorption of macromolecules within the pores is favoured by the molecular-sieve effect. Over a wide range of energies, a continuous transition occurs from gel-permeation chromatography, in which the components are separated mainly owing to the macromolecular-sieve effect, to adsorption chromatography, in which the separation is due mainly to differences in the adsorption of components of different molecular weight. A linear calibration of K d is possible as a function of MW, within the limits of a given homologous series, and itis desirable to use this calibration both for gel-permeation and for adsorption chromatography of polymers.