The 0-' chemical ionization (CI) mass spectra of the mono-to pentafluorobenzenes, fluorotoluenes and fluoroanisoles were measured. For comparison, the 0-' CI mass spectra of toluene (including deuterium-labelled variants) and anisole were also measured. The major reaction channels of 0-' with fluorobenzene involve H-atom displacement and H: ' abstraction. With increasing fluorine substitution H + abstraction increases in importance. For the tri-and tetrafluorobenzenes HZ' abstraction is important only when there are two hydrogens ortho to each other. Reaction channels which are unique to the fluoroaromatic molecules involve the formation of [ M + 0 -HFI -., which, for polyfiuoro compounds, fragments further by elimination of H F or CO. For the fluoroanisoles, formation of FC,H,O-and elimination of CH,O from [ M -HIand [ M -2H]-. are important reaction channels. The formation of [ M + 0 -HIby reaction of 0-' with toluene is shown to involve specific displacement of a ring hydrogen, whereas the formation of [ M -H 1 -involves primarily abstraction of a proton from the methyl group. By contrast, H: ' abstraction is non-specific and proceeds by three pathways: (i) abstraction of two hydrogens from the aromatic ring, (ii) abstraction of two hydrogens from the methyl group and (iii) abstraction of one hydrogen from each position; however, the resuls are not in accord with a random selection of hydrogens.