Plants belonging to the Thalictrum L. species contain numerous basic components representing various types of structure. The identified compounds belong to the following groups : (I) isoquinoline alkaloids, 2 substances; (II) benzylisoquinoline alkaloids, 2 substances; (III) aporphine alkaloids, 8 substances; (IV) bisbenzylisoquinoline alkaloids, 15 substances; (V) aporphinobenzylisoquinoline alkaloids, 4 substances; (VI) hexahydrotriphenilidine alkaloids, 2 substances; (VII) protoberberine alkaloids, 9 substances, and, (VIII) glucoalkaloids, at least 46 substances altogether. The majority of the alkaloids consists of tertiary compounds, the rest is composed of quaternary substances ; the separation of both types takes place during extraction or purification of the extracts. In the course of investigating the compounds contained in the roots of Thalictrum minus L. var. datum Koch. a fraction of tertiary products was obtained which showed 11 spots on the chromatograms. The fraction yielded two products identified as aporphinobenzylisoquinoline alkaloids : a new alkaloid thalmineline, the structure of which could be fully elucidated, and another product designated 'compound C'. The eleven-spot fraction of quaternary bases yielded berberine, magnoflorine, jatrorrhizine, and thaliphendine as pure substances. The initial tests on the constituents of the above-mentioned plant were carried out by thin-layer chromatography (TLC), the details of the procedure being worked out with standard substances, including 16 tertiary bases and 6 quaternary ones, obtained from various research centres.