This study was performed to quantitate vascularity in periprosthetic tissues of loose total hip replacements (THRs), because most likely revascularization and endothelial cells are important for implant osseointegration and loosening. Interface and pseudocapsular tissue samples obtained from loose THRs were stained with an immunohistochemical labelling (ABC technique) for von Willebrand factor. Non-inflammatory synovial samples served as controls. The results were quantitated by morphometry using the Kontron image analysis system. Evaluation of the mean endothelial index (EI; positively stained area micron/mm2 of tissue) revealed that in the control samples synovium was better vascularized than was the case in the cellular areas of the periprosthetic pseudocapsule (P = 0.0008) and interface (P = 0.0004) of loose THRs. There was no significant difference between mean EI of cellular areas in the interface and that of the pseudocapsule (P = 0.24). In the interface the vascularity was irregular. Vascular injury and decreased blood supply seem to occur at the implant-host interface, which may be one of the reasons for insufficient implant osseointegration and loosening.