Strontium isotope ( 87 Sr/ 86 Sr) signals and trace elements have been measured in fossil fishes in order to evaluate their suitability as palaeoenvironmental markers of their original habitats, while accounting for post-depositional alteration. Preliminary physical and chemical characterization of both Recent and fossil fish teeth from marine and freshwater environments have demonstrated differences in their respective biological properties, largely defined by their environment, and differences in post-depositional (diagenetic) alteration. A range of well-provenanced modern and fossil fish teeth dating back to the Eocene (55 Ma) have been subjected to a series of sequential washes in a mild acetic acid buffer in order to remove adsorbed and exchangeable ions of diagenetic origin from mineral surfaces and exchange sites, and to dissolve calcite overgrowths. The leaching protocol is designed to separate carbonate, hydroxy- and fluorapatites on the basis of differential solubility and relative crystallinity. The relative solubilities of enamel, dentine and whole tooth samples of fossil fishes would appear to correlate with those observed for modern biological apatites. Furthermore, a highly soluble strontium-rich phase is washed out of the majority of samples which may effect significant changes to their 87 Sr/ 86 Sr signal. Studies have focused on Cenozoic fish material where the 87 Sr/ 86 Sr seawater curve is well-constrained, but there is little absolute or quantitative congruence with this reference. However, relative or qualitative trends in 87 Sr/ 86 Sr signals of samples representing presumed marine-fresh water transitions suggest that biogenic signals can potentially be recovered from palaeontological material with continued leaching to remove the diagenetic overprint.