Up to now, sixteen gibberellins have been isolated and their structure established. Mass spectroscopy of these large number of gibberellin homologues should afford useful information not only for identification but also for structural elucidation of new gibberellins. Recently Wulfson et al. (1) reported the mass spectra of methyl esters of gibberellins Al, A3 and AL, and discussed possible fragmentation process. Now we wish to present our result concerning high resolution mass spectra of twelve Cl9 gibberellin homologue methyl esters shown in Fig. 1. Our objective in this research is to determine fragmentations, which are characteristic to the common structural features, as well as structural modifications in gibberellins. The mass spectra were obtained by Mattauch-Herzog type spectrographs (CEC Zl-1lOB and JNS-OlS), with direct inlet system, under following co&it_sns: Electron accelerating voltage, 70 eV; temperature of ionization source, l&O-160~; temperature of vaporization, lOO-130". Based on Biemann's procedure (21, element maps were prepared. Results are summarized in Table 1, in which compositions of prominent fragment ions in high mass region are expressed as M-X (X:lost mass). Most Cl9 gibberellin methyl esters exhibited parent peaks having moderate intensity, and prominent peaks due to M-32(CH,+O), M-46(CH202), M-60(C2HL02), M-78(C2H603) ,