Enthalpic phenomena were shown to contribute to the size exclusion separation mechanisms during chromatographic analysis of solutions of pullulan and cellulose in LiCl-N,N-dimethylacetamide (LiCl-DMAc) solvent and eluent. The effect of LiCl concentration in the sample solutions and the effect of temperature were of the same order of magnitude for both pullulan and cellulose samples. This led to systematic errors in the determination of mean molecular mass in the range of tens of percent, depending on the chromatographic conditions and on the molecular mass of the analyte. The systematic error is much higher than the random errors; the typical values of the latter being up to a few percent (RSD). Low column temperature and a higher content of LiCl in the sample solution led to lower determined mean molecular mass values. This can be explained by a decrease in the interactions between dissolved macromolecules, although polymer-stationary phase interactions should also be taken into account. Furthermore, the cellulose stability in solution was determined: the zero order random degradation constant being k = 6.9 x 10(-8) mol mol-1 monomer day-1.