The three terminal capacitance dilatometer is the most sensitive means for measuring the thermal expansion of solid samples at low temperatures. A measuring system based around capacitance dilatometry has been automated to provide a means of routine data collection of length changes in samples in the temperature range 1.5 K to 300 K. The dilatometer has been used in conjunction with magnetisation and neutron scattering measurements to investigate members from rare earth alloys as part of a wider study of the magnetic and lattice properties of isostructural rare earth alloy series, in particular the rare earth alloy series RE2AgIn (RE = Tb, Ho and Er) and REPtIn (RE = Nd, Gd, Tb, Dy, Ho and Er). Two samples have been investigated using thermal expansion, Tb2AgIn and TbPtIn. Both order magnetically at temperatures around 50 K and phase transitions corresponding to the ordering were observed using the capacitance dilatometer for the samples. The data for the alloy series is presented and discussed with a view to describing the complex nature of these alloy systems.