1.Based on the experimental determination of the retention indices of the methylpyridines, the retention indices of six dimethyl and trimethyl pyridine derivatives have been determined with good accuracy by taking into account the nonadditive change of the energy of sorption of methylene groups.2.The calculated values of the retention indices can be used for identifying methyl-substituted pyridines in complex mixtures for analyses performed on glass capillary columns with OV-101, OV-17, and PÉG-40M.3.The deviations from additivity of the energy of sorption of methyl-substituted pyridines have been thermodynamically evaluated, and data on the dispersion nature of this phenomenon have been obtained