EPR spectra at 9. 1 and 30 GHz are reported for the iso-electronic ions Gd**3** plus and Eu**2** plus in glasses of composition 0. 50 ZrF//4, 0. 20 BaF//2, 0. 055 AlF//3, 0. 045 LaF//3 and 0. 10 NaF or LiF. The spectra are similar to the 'U' spectra familiar in many oxide glasses, indicating very low and disordered site symmetries with a broad distribution of crystal fields. For europium the mean ... [Show full abstract] crystal-field parameter, b//2**0 approximately equals 0. 075 cm** minus **1, is 30% larger than that for gadolinium, b//2**0 approximately equals 0. 058 cm** minus **1, suggesting that the two ions occupy significantly different sites. Whereas the trivalent gadolinium will substitute readily into La**3** plus sites, it is likely that divalent europium ions replace Ba**2** plus in sites where they are more weakly bound and have a higher fluorine coordination.