The systematic approach described for investigating basic (pharmaceutical) drugs with the aid of paper and thin-layer chromatography relies on the principle that the positions of the spots created by a certain substance on various chromatograms in relation to 5 to 7 test substances and developed together with the sample are indicated by a digit code. With a pre-determined sequence of application of the solvents, code numbers are formed by writing down these digits (supplemented by indices), which are characteristic of the components of the mixture. The code numbers are in all cases clearly distinctive even in the case of a large number of different substances (e.g. 300) if the number of appropriately chosen developing solutions is increased to 6. Evaluation of the code numbers can be carried out with tables or with the aid of punch cards.