The effect of hydrostatic pressure on the ionic conductivities and phase transitions in PbF2 and SrCl2 has been investigated. The cubic to orthorhombic transition in PbF2 was studied in the temperature range of 300 to 850 K for pressures up to 0.55 GPa; the similar transition in SrCl2 was investigated in the range 500 to 1050 K for pressures to 0.45 GPa. The transition temperature was seen to increase linearly with increasing pressure at higher temperatures in both materials. There is considerable hysteresis in the transition at lower temperatures. The activation volumes were extracted from the effect of pressure on the conductivity. The volumes are small at all times, and are consistent with the dominance of Frenkel defects in these materials. © 1980 The American Physical Society.