The method of CERMAK and HERMAN has been applied to mass spectrometric studies of symmetrical electron and proton transfer processes. The characteristics of the ion source used have been investigated both experimentally and theoretically. A new type of ionization efficiency curve is obtained if the current o secondary ion is plotted as a function of the voltage between ionization chamber and electron trap at constant low voltage between the filament and the chamber. Essentially complete discrimination of primary ions has been achieved. Electron transfer occurs with rather low cross section in methane but increases with molecular size and with increasing unsaturation. Large cross sections were observed in sulfur and iodine containing compounds. Double charge transfer reactions such as NO++ + NO → NO + NO++, Xe++ + Xe → Xe + Xe++ have also been observed. Proton transfer reactions have been observed in several simple molecules. Some experimental results are presented which indicate that proton transfer may occur via a complex (at low kinetic energies) or as a stripping process (at higher energies). Fragment ions have also been observed in the secondary mass spectra of several compounds. While part of these may result from the scattering of primary fragment ions, in some cases additional processes have to be postulated such as hydride ion transfer and dissociative charge transfer from vibrationally excited ions.