Bone diagenesis is a set of processes by which the organic and mineral phases and the structure of bone are transformed during fossilization. To understand how these processes have affected skeletal material recovered from Azokh Caves (particularly the organic preservation), we measured ‘diagenetic parameters’ of skeletal material from Holocene, Late Pleistocene and Middle Pleistocene deposits from Azokh Caves. Additionally, we used this study to further test the application of both nitrogen adsorption isotherm analysis and mercury intrusion porosimetry for measuring the porosity of fossil bone. The skeletal material from the Pleistocene layers of Azokh Caves can be characterized as generally poorly preserved (especially collagen preservation). Porosity values of the bones are lower than might be expected as many bones show evidence of extensive infilling of the pores with secondary minerals. The pore infilling in the Middle Pleistocene layers is most extensive and this type of preservation has not previously been described in archaeological material.