Carbon and nitrogen stable isotope ratios of bone and tooth dentine collagen from 142 horses were analysed to consider the potential of isotopic analysis of faunal remains as a palaeoenvironmental and palaeoclimatic proxy. A general trend through time towards lighter δ 1 3 C values was observed, but with an obvious depletion at the Late Glacial/Holocene transition. Horse δ 1 3 C values appear to track plant δ 1 3 C. Although phenomenon such as the canopy effect may influence faunal δ 1 3 C values, we believe that the influence on plants of increasing atmospheric CO 2 is the primary factor in the change in faunal δ 1 3 C values at the Late Glacial/Holocene transition. A post-glacial depletion in horse δ 1 5 N values is observed in areas proximal to glacial retreat although no data is available in these areas during the Last Glacial Maximum. Horse δ 1 5 N values are presumed to reflect plant δ 1 5 N values. Depleted plant nitrogen may be attributed to a number of factors e.g. water availability, temperature, cycling of nitrogen in the soil, soil nutrient availability (especially phosphorus in the post-glacial period), and the type of mycorrhizal associations formed with plant. These effects may be interrelated, and be linked such that a positive feedback can give a non-linear response to a single parameter.