A new dihydroindole alkaloid, 'bannucine,' has been isolated from the leaves of Catharanthus roseus (L) G.Don, and has been found to have a five-membered lactam ring attached to the vindoline moiety. Catharanthus roseus (L) G.Don (Apocynaceae) is widely distributed throughout Pakistan. It is used in the Unani system of medicine as a hypoglycaemic agent. The plant has been extensively studied during the last two decades, primarily on account of its antitumour properties. A large number of alkaloids have previously been reported from this plant of which vinblastine and vincristine are widely used in the chemotherapeutic management of a wide variety of human neoplasms. We have previously reported several new alkaloids from the leaves of C. roseus. Our continuing studies on the plant have resulted in the isolation of a novel Aspidosperma alkaloid, which we call bannucine, to which structure (1) has been assigned.