Chromatographic indexes that facilitate a better reproducibility of paper chromatographic results have been proposed, using the homologous series of coloured derivatives of secondary amines as standard substances. When using dimethylformamide as the stationary phase the value of the indexes proved to be independent of the concentration of the impregnating solution of the stationary phase, of the temperature changes during the chromatographic process, of the ways of impregnation and of the skills of workers. It depends only on the type of the stationary phase and on the composition of the mobile phase. The obtained indexes can contribute to a better reproducibility of RF values and to an easier and more objective identification of substances.