A defatted ethanolic extract of the roots of Thalictrum foliolosum DC. (Ranuculaceae) afforded the alkaloids thalrugosidine (1), thalrugosaminine (2), thalisopine (thaligosine) (3), thalirugidine (4), oxyberberine (berlambine) (5), and noroxyhydrastinine (6) after the usual systematic partitioning and chromatographic procedures. Thalictrum foliolosum DC. (Ranunculaceae) is a tall perennial rigid herb indigenous to the temperate Himalayas (5000-8000 ft) and the Khasia hills (4000-6000 ft) of India. Extracts of the roots have been used by the natives as a tonic, febrifuge, diuretic, cathartic, and a collyrium for the improvement of eyesight as well as in the treatment of flatulence, jaundice, and visceral obstructions (1, 2). Although the literature is abundant with numerous chemical and phytochemical studies of various Thalictrum species (3-5), the only references to previous work on T. foliolosum reported the isolation of the quaternary protoberberine alkaloids berberine, jatrorrhizine and palmatine (6) and the quaternary aporphine alkaloid magnoflorine (7, 8) from extracts of the rhizomes. The genus Thalictrum has been a particularly rich source of benzylisoquinoline-derived alkaloids with over 100 different alkaloids having been isolated and characterized by the end of the last decade (9). The multiplicity of types of benzylisoquinoline-derived alkaloids isolated from Thalictrum species include monobenzylisoquinolines (4), isoquinolones (4), protoberberines (4), aporphines (4, 10), dehydroaporphines (10), oxoaporphines (4, 10), pavines (4), isopavines (4), protopines (4), phenanthrenes (4, 10), bisbenzylisoquinolines (3, 5), aporphine-benzylisoquinoline-dimers (4, 11), dehydroaporphine-benzylisoquinoline dimers (4, 11), proaporphinebenzylisoquinoline dimers (11), and appropriate-payine dimers (11). A number of these bases have been found to exhibit hypotensive activity in normotensive animals and antimicrobial activity against selected mycobacteria and fungi (12-14). It was decided to undertake a phytochemical investigation of the alkaloids of T. foliolosum because of the paucity of reports in the literature concerning this species and to seek a source of compounds with potential biological activity. This paper is to report the isolation and identification of thalrugosidine (1), thalrugosaminine (2), thalisopine (thaligosine) (3), thalirugidine (4), oxyberberine (5), and noroxyhydrastinine (6) from extracts of the roots of T. foliolosum. The dried, powdered roots of T. foliolosum were defatted with petroleum ether and extracted by percolation with ethanol. The ethanol extract was evaporated to a thick syrup, treated with aqueous citric acid, and filtered. The filtrate was partitioned with chloroform (Fraction A), alkalinized with ammonium hydroxide and repeatedly extracted with ether (Fraction B). The combined ether extracts (Fraction B) were chromatographed over neutral alumina in chloroform to afford the bisbenzylisoquinoline alkaloid thalrugosidine (1). This alkaloid was first isolated from extracts of T. rugosum in 1972 (12) and, to our knowledge, this constitutes only the second reported isolation of this base from nature. Thalrugosaminine (2) was isolated from Fraction B; this alkaloid exhibited hypotensive activity in rabbits (14) and antimicrobial activity against the acid-fast rod Mycobacterium smegmatis (14, 16). Thalisopine (3) and thalirugidine (4) were also obtained from Fraction B. Oxyberberine (5) and noroxyhydrastinine (6) were isolated from Fraction A. In summary, the isolation of thalrugosidine (1), thalrugosaminine (2), thalisopine (3), thalirugidine (4), oxyberberine (5), and noroxyhydrastinine (6) from T. foliolosum constitutes the first report of any nonquaternary alkaloid from this species and further supports the overall chemotaxonomic character hitherto established for the genus Thalictrum.