Fragmentation of secondary and tertiary γ-aminopiperidines proceeds via elimination of γ-amino radicals and the ring substituents of piperidine, and is accompanied by their cleavage. High-resolution mass spectral data, DADI spectra, and fragmentation of deutero analogs confirm this decomposition. On the basis of quantum chemical MNDO calculations the most probable alternate structures have been proposed for a number of typical ions. From the features of dissociative ionization we can determine the kind and location of substituents in the piperidine ring. © 1990 Plenum Publishing Corporation.