Two crystalline, non-phenolic alkaloids, of formulas C22H28N2O4 and C22H26N2O6 respectively, have been isolated from the leaves of Mitragyna rotundifolia. The former is identical with rhynchophylline of Hondo and mitrinermine of Raymond-Hamet, while the latter appears to be new and is named rotundifoline. Both alkaloids are methyl esters, and each contains in addition a methyl ether grouping; methylenedioxy and =NCH3 groups were found to be absent. In rhynchophylline three of the oxygen atoms are accounted for; the nature of the fourth is unknown. Similarly in rotundifoline, the function of only three of the five oxygen atoms has been determined. The absorption spectra of rhynchophylline and rotundifoline have been compared with that of yohimbine. Distillation of rhynchophyllic acid with calcium oxide yielded a neutral substance of formula C10H9NO. Rotundifolic acid, on the other hand, was merely decarboxylated under these conditions with the formation of a crystalline base, C2OH24N2O3. Degradation of rhynchophylline and rotundifoline with soda-lime gave mixtures of oxygenated indoles and pyridine-like bases, from which, in the case of rhynchophylline, a base of probable formula C8H9NO, was isolated. From selenium dehydrogenation of rotundifoline, a base resembling pyridine, of formula C9H13N, was obtained. © 1939, American Chemical Society. All rights reserved.