The use of enamel phosphate oxygen from small mammal teeth in Eocene palaeoclimate research is discussed and its future potential application to Quaternary palaeoclimate research is considered. With reference to published work and additional results presented here from the Late Eocene (Priabonian) Headon Hill Formation of the Hampshire Basin, it is shown how a new direct laser fluorination technique can be used to determine the enamel phosphate oxygen δ 1 8 O value from teeth of the rodents Thalerimys and Isoptychus. It is shown how these values can be used to calculate a mean palaeo-δ 1 8 O local freshwater value, which can be used to calculate a mean annual temperature. The local water value can also be combined with other specific freshwater palaeoproxies to calculate mean palaeotemperatures for the growing season and the warmest months of the growing season. Additional results presented specifically in this paper are (1) oxygen isotope results that indicate that Thalerimys teeth with etched enamel, indicative of digestive activity, have not experienced isotopic fractionation; (2) moulding of Thalerimys teeth to produce a solid 3D record prior to sample preparation and analysis does not affect their enamel phosphate oxygen isotope values. Both of these new results enhance the potential application of the method by making more fossil tooth material available for study.