Cultured endothelial cells are used as tools to study the involvement of endothelium in various physiological and pathological processes. Significant physiological differences exist among endothelial cells from different districts. Microvascular endothelium is an integral part of bone tissue. Bone endothelial cells have been cloned from fetal bovine sternum. They show differentiated characteristics and a novel response to parathyroid hormone. This 'in vitro' model will make possible the analysis of possible influences of the endothelium on bone formation and resorption. The possibility that bone endothelial cells actively participate in the bone remodelling process is proposed.