The Hall mobility of electrons and holes in CaF2 (0.005% Tb) was measured under illumination by near-uv radiation (3100-4000 Å) in the temperature range 25-200°C. At 334°K =12θLO, the maximum measured mobilities were 236 and 100 cm2V-1sec-1, respectively, for electrons and holes. These magnitudes are consistent with those predicted by wide-band optical-phonon theories (large polaron). Upper limits of m*<=0.12m and m*<=0.21m were estimated respectively for the electron and hole band masses. Because of two-carrier effects, it was not possible to determine whether the charge transfer during the photochromic process occurs via the conduction or valence bands.