Molar enthalpies of mixing of the LiBr-LaBr3, NaBr-LaBr3, KBr-LaBr3, RbBr-LaBr3 and CsBr-LaBr3 systems have been measured with a Calvet-type high-temperature micro-calorimeter. The enthalpies decrease gradually from -0.67 kJ mol(-1) for the lithium system through -4.32, -10.73 and -14.97 kJ mol(-1) for the sodium, potassium, and rubidium systems to -16.81 kJ mol(-1) for that of cesium at the composition of the 3 MBr . LaBr3 compound. The results have been discussed in terms of the conformal solution theory of Davis as well as in terms of relative ionic potentials.