<jats:p> The alkaloids tuberostemonine, oxotuberostemonine, and the new base tuberostemonine-A have been isolated from the rhizomes of Stemona sessilifolia. Tuberostemonine has been oxidized to oxotuberostemonine and tuberostemonine-A has been related to tuberostemonine through common oxidation products. Study of transformation products of tuberostemonine has enabled assignment of partial structure V to the alkaloid.