It is shown that in chromatography of flexible chain polymers on macroporous, swollen absorbents the components are separated in the main by two mechanisms, namely the molecular sieve and occlusion mechanisms. The latter is dependent on the thermodynamic compatibility of the polymer molecules with the absorbent matrix. Macromolecules that are incompatible with the absorbent are completely excluded from the compact regions of the latter, while compatible macromolecules are able to penetrate into these regions, which affects the retention volume and results in deviation from Benoit's principle of universal calibration. The exclusion effect can be described by analogy with the exclusion volume of polymer molecules and thus enables information to be obtained about the constants of interaction of polymer segments with one another, with the absorbent and with the solvent, by the use of gel permeation chromatography.