The bimolecular gas-phase reactions of d-block transition-metal cations M(+) with dimethyl peroxide were screened by means of Fourier transform ion cyclotron resonance mass spectrometry. The rich chemistry can be classified into four types of reactions: i) Oxygen-atom transfer to generate MO(+), ii) elimination of radicals, mostly CH3O., iii) intramolecular redox reaction of dimethyl peroxide to form CH3OH, CH2O and CO, and iv) charge transfer from the metal cation to produce CH3OOCH3+. Some general trends became apparent from this study. For example, the ''early'' transition metals almost exclusively induce oxygen transfer to generate MO(+), in line with the notoriously high oxophilicities of these metals, and electron transfer is only observed for Zn+ and Hg+. Both the radical loss and the disproportionation reaction emerge from a rovibrationally highly excited insertion intermediate (CH3O)(2)M(+), and for the first-row metals the branching ratio of the competing processes seems to be affected by the M(+)-OR bond strengths as well as the electronic groundstate configurations of M(+). For the 4d and 5 d cations Ru+-Ag+ and Pt+-Au+, respectively, products resulting from intramolecular redox reactions dominate; this probably reflects the higher propensity of these metal ions to facilitate beta-hydrogen atom shifts.