Fishmonger’s Swallet, Alveston, Gloucestershire, has produced an unusual quantity of human and animal bone dating to the Late Iron Age. Iron Age burial evidence in the south-west of Britain is scarce and human remains in caves are rarely considered due to lack of secure dating evidence, so the material from this site offers rare insights into a poorly understood mortuary practice. However, the nature of deposition within the cave is unclear as the remains are disarticulated and heavily fragmented. This paper presents an interim report on an ongoing histological study of bone diagenesis of human remains from Fishmonger’s Swallet. The amount of bacterial bioerosion and fungal tunnelling in bone microstructure was assessed in seven human remains excavated from the cave in 2000-01 to examine early post-mortem treatments. The results of this analysis, considered alongside taphonomic observations by Cox and Loe (2022, this volume), indicates that the individuals were subject to a variety of post-mortem treatments prior to interment within the cave.