A new guanidine-type alkaloid, fontaineine (1), was isolated from the leaves of Fontainea pancheri and its structure elucidated by 2D NMR. During the course of a systematic search of alkaloids in New Caledonian plants,1 we have isolated from the leaves of Fontainea pancheri (Baillon) Heckel, a new acyclic guanidine-type alkaloid, fontaineine (1). The genus Fontainea belongs to the family Euphorbiaceae, subfamily Crotonoidae. Guanidine alkaloids with related structures were reported from two plants of this subfamily, Alchornea floribunda2 and Alchornea javanensis.3 However, they differ from compound 1, showing the guanidine included in two rings or only simple chains.