Studying stable isotopes in tree rings allows the reconstruction of past climate with annual resolution and statistically defined confidence limits1 . A system has been developed by Sercon and Swansea University which allows the measurement of δ13C values in tree rings via laser ablation – combustion – GC – IRMS. When this information is combined with EA-IRMS measurements of δ13C values in leaves, this allows an evaluation of post-photosynthetic fractionation processes occurring at leaf level and downstream at high resolution during a growing season, and so the intra-annual pattern of δ13C variability can be studied. Furthermore, when combined with δ18O and δD measurements made via pyrolysis-IRMS, a multi elemental and isotopic study can be assimilated to reconstruct past climate, the reader is referred to applications note 023 for more details on the other instrumentation which can be used. This applications note describes the system Sercon have developed at Swansea University, and goes on to describe the modifications made in collaboration with Teledyne Cetac. As the two leading manufacturers actively involved in development of the laser ablation – IRMS system, we are hosting workshops on the technique and invite researchers to collaborate with us, send us their samples, and explore whether this novel technique can be used to expand the research capabilities of their l