The middle Pleistocene sequence at the Atapuerca (Burgos) complex of caves is most completely represented at Gran Dolina. Eleven stratigraphic units are distinguished, seven of which contain abundant small mammal fossils. These seven units are analysed in order to determine the taphonomic processes present during the accumulation of their faunal remains. The fossil bones are extensively broken, both before and after burial. Fossils from six of the units show evidence of localized pre-depositional acid corrosion, which occurred both before and after breakage. In the upper levels, there is also evidence of post-depositional corrosion, both from alkaline and from acid environments of deposition, and in the top level some fossil bones also show evidence of weathering and root marks. Images of these modifications, by means of the scanning electron microscope, and their comparison with a large comparative data base of recent modifications from known causal agents, permits the identification of the agents responsible for many of the modifications, and consequently the reconstruction of the sequence of events leading to the accumulation and preservation of the fossil assemblages. Predators are implicated for some of the breakage and all of the pre-depositional corrosion, which is the result of digestion in the predators' stomachs. In all cases the category of predator can be identified, and at three stratigraphic levels the actual species can be identified with moderate degrees of reliability. Post-depositional corrosion is linked with observations on local acidity/alkalinity of different levels, and the incidence of weathering is linked with evidence for roof collapse over parts of the cave. Taking account of the effects of these processes, particularly the selectivity resulting from predator hunting methods, allows estimates to be made of the degree of bias in the faunal composition and the palaeoecology thereby indicated.