The leaves of Holarrhena crassifolia Pierre (Apocynaceae) from Laos and Cambodia have been found to be particularly rich in alkaloids of the conkurchine type. This discovery is an argument for maintaining the species H. crassifolia, which has been confused with H. curtisii King and Gamble, an apocynaceous species from Malaysia which contains alkaloids of a different type. The structure of a new alkaloid, N-formyl-conkurchine is described and the reactivity of its functional groups outlined. © 1972.