The alkaloids of the leaves and bark of several species of Mitragyna have been examined as a preliminary to a more intensive chemical study of compounds of this class. Rotundifoline has been extracted from the leaves, and rhyncophylline from the bark, of M. ciliata. The identity of rhyncophylline with mitrinermine, suggested by Raymond-Hamet and supported by Barger et al. but disputed by Millat, has been established. A new phenolic alkaloid, mitragynol, has been isolated from M. rotundifolia; its methyl ether has been shown to be identical with dihydrorotundifoline. The hitherto unknown dextro-form of mitraphylline has been isolated from M. rubrostipulaceæ. Evidence has been obtained that the base, C9H13N, obtained by Barger et al. by selenium dehydrogenation of rotundifoline is 3:4-diethylpyridine. Quinovic acid has been extracted from both leaves and bark of several species of Mitragyna, and a sterol from the bark of M. inermis has been identified as β-sitosterol.