A new binary indole alkaloid, leurosinone, has been isolated from the leaves of Catharanthus roseus, and has been assigned structure (1) on the basis of spectral studies. Catharanthus roseus (L) G. Don (Apocynaceae) is widely distributed throughout Pakistan. A number of indole and binary indole alkaloids have previously been reported from this plant of which vinblastine (VLB) and vincristine play an important part in human chemotherapeutic. During studies on this plant, we have isolated a new binary alkaloid, leurosinone, to which structure (1) has been assigned on the basis of n.m.r. studies including homodecoupling experiments. Its stereochemistry has been determined by a series of n.0.e. difference measurements and 13C n.m.r. assignments made by DEPT pulse sequence and GASPE experiments.