The magnetic parameters derived from the e.s.r. spectrum of XeF in γ-irradiated XeF2 at 77 K are comparable with those previously derived for this radical in XeF4. Small differences can be adequately explained in terms of minor librations in XeF4. The results are compared with those for VK centres in alkali halides and environmental effects for these radical anions are discussed. Spin-densities calculated from the 19F and 129Xe atomic values suggests that the unpaired electron is in an orbital comprising 2s and 2p AOs on fluorine and 5s and 5p AOs on Xe. There is no need to invoke participation of the Xe 5d level, and any large admixture is improbable.