Structures of three Stemona alkaloids from a Chinese medical plant are described. Both stemotinine 1 and isostemotinine 2 isolated from the roots of Stemona tuberosa Lour. (Stemonaceae) are shown to be pentacyclic compounds containing two α-methyl-γ-lactone rings; the structure fo stemonidine isolated in 19481 has also been determined as 3. Structure elucidations are based on detailed 1H- and 13C NMR studies. A preliminary account is given on a line-broadening effect of 1H NMR signals which are in spatial proximity with incipient N+D bonds. © 1982.