DNA-recombinant studies have established that factor VIII-mRNA is present in liver and placental tissue. In a previous immunohistological study using monoclonal antibodies we have localized factor VIII in liver sinusoidal endothelial cells. In this paper we demonstrate that also the endothelial cells lining the fetal vessels in human placenta contain factor VIII. Based on the combined results of the present study and a previous study we favour the concept that factor VIII is synthesized in placental endothelial cells.