The cation radicals of simple alkyl hydroperoxides ROOH(+.) (R = CH3, C2H5, iso-C3H7, tert-C4H9) have been studied by various mass spectrometric techniques, and neutralization-reionization (NR) methods in particular. Collisional activation (CA) of the beam of fast neutrals before reionization (NCR) and collision experiments with the mass-selected survivor ions (NR/CA) demonstrate that the peroxide O-O bond remains intact in ionized methyl hydroperoxide. In the series of hydroperoxides, the abundances of the survivor ions decrease with a-substitution, which can be traced back to increasing contributions of [R(+)/(OOH)-O-.] ion/dipole complexes to the parent ion beam. For the elucidation of ion structures, (+)NR(-) experiments are shown to be particularly helpful, in addition, they also provide insight into the bonding situations in hydroperoxides. Unimolecular loss of H-. from metastable ions (MI) of CH3OOH+. leads to hydroperoxy methyl cations, CH2OOH+, which are characterized by their MI/CA mass spectra. For comparison, four distinguishable [C,H-3,O-2](+) isomers (CH2OOH+, CH3OO+, HC(OH)(2)(+), and H3O+. CO) have been generated and examined by MI, CA, and NR experiments. With the exception of the proton-bound species H3O+. CO, the corresponding neutral [C,H-3,O-2](.) radicals exist as well and do not interconvert into each other. In addition, HOCH2O. radicals can be probed by (-)NR(+) experiments with HOCH2O- anions. Unimolecular and collision-induced decomposition of CH2OOH+ gives rise inter alia to a composite [C,H-2,O](+) peak: which consists of a narrow gaussian and a broad, dish-topped component. The narrow component vanishes in the (+)NR(+) experiment.