The M+ and [M-H]+ ion peaks are the peaks of maximum intensity in the mass spectra of Schiff bases belonging to the 4-aza-9-fluorenylidenearylamine series. The dependence of the relative intensity of the [M-H]+ fragment on the structures of the I-XI molecules provides evidence for the possibility of the occurrence of rearrangement processes involving the formation of this ion. The formation of [M-CH3]+, [M-HCN]+, [M-Ar]+, and [M-CNAr]+ ions is also characteristic for the fragmentation of the investigated compounds. It was found that, in contrast to other types of Schiff bases, the ejection of an HCN molecule during the mass-spectrometric fragmentation of the investigated compounds occurs without participation of the nitrogen atom of the azomethine group. The elimination of a CNAr particle by the molecular ions is a distinctive feature of the investigated series of Schiff bases. © 1979 Plenum Publishing Corporation.