Updated project metadata. Liver transplantation is the only treatment option for patients with end-stage liver disease. However, a persistent disparity remains between supply and demand for donor organs suitable for transplantation, resulting in a waiting list mortality of up to 20%. This has resulted in an increasing use of high-risk grafts from suboptimal, extended criteria donors, including livers from donation after circulatory death (DCD) donors, and donors with significant comorbidities such as advanced age, diabetes mellitus and livers with high fat content. While cold storage remains sufficient for livers considered optimal for transplantation, ECD grafts are more vulnerable to cold ischemic damage, resulting in many of these grafts being rejected. As an alternative to cold storage, ex-situ normothermic machine perfusion (NMP) has become an increasingly popular method for preservation, transportation and assessment of ECD livers prior to transplantation. This allows for functional assessment of the graft and provides the opportunity to assess key processes that can be used to determine organ viability. The use of both hepatocellular and biliary viability criteria in selection of suboptimal livers from ECD donors has led to the successful transplantation of these grafts with a low incidence of post-transplant cholangiopathies. However, the mechanisms of biliary injury, and recovery thereof, following static cold storage remains poorly understood. Insight into these mechanisms may further improve preservation and selection of ECD livers. Therefore, we performed an in-depth proteomics analysis of bile samples collected from human ECD livers during NMP to identify potential mechanisms linked to biliary injury, function and regeneration over the course of the perfusion, and to assess whether biliary protein profiles can distinguish between transplantable and non-transplantable grafts.