This paper assesses the preservation of bones exposed on the floor of Chauvet Cave. These bones are mainly from cave bears. They exhibit very variable macroscopic preservation, from apparently pristine specimens to those that are decomposing or coated with calcite. This site offers a unique opportunity to investigate, on a large scale, bone diagenesis in a karstic context. Despite the highest priority put on the preservation of the cave features, about one hundred bone fragments from most sectors of the cave could be collected for biogeochemical investigation. Carbon and nitrogen elemental content were measured, and X-ray diffraction spectra were established. Only about one quarter of the specimens yielded collagen that retained its biogenic isotopic signatures. Bones exhibiting different stages of preservation were not randomly scattered in the cave. Local environmental conditions seem to have led to different diagenetic pathways. Widely differing states of preservation were seen in bones of similar age. This site provides a good case study of diagenetic process occurring in karstic sites and may be used to better understand diagenesis in less well studied caves.