The possible Beckmann rearrangement of aryl heteryl ketoxime ions has been investigated by studies on the 70 eV mass spectra, metastable ion spectra and collision induced dissociation spectra of pairs of isomeric ketoximes and corresponding amides. Aryl cycloalkyl ketoximes were also studied, and the molecular ions of these and the corresponding amides showed no evidence of interconversion. The introduction of the heterocyclic moieties made little change to this situation although some novel rearrangements were observed.