The role of glomerular endothelium has been barely considered, let alone investigated, but this is in large part due to the extreme difficulty in isolating and growing it in culture. The glomerular capillary is part of the arterial system and is better perceived as a "hemiarteriole." The mesangium and its response to hemodynamic events in the glomerular capillary is equivalent to the smooth muscle cell wall of an arteriole. The capability of cytokines, derived from the endothelium, to act in an autocrine and paracrine manner is clearly demonstrated by angiogenesis. The glomerular endothelial cell is likely to play a crucial role in the glomerulus in health and disease.