We have identified several antibodies which in immunocytochemical experiments reveal antigenic heterogeneity in renal vascular endothelium. In the renal vascular endothelium, blood group antigen H type II was carried in a sialylated form on an endogalactosidase resistant molecule. The glomerular reactivity was sensitive to digestion by this enzyme. Monoclonal antibodies of the CD 39, CD 14, and CD 11C leucocyte differentiation clusters bind to renal vascular endothelium but not to glomerular capillaries. In fetal kidney, the developing glomerular endothelium has the same phenotype as the remainder of the vascular tree with respect to these markers. There are therefore antigenic differences among renal endothelial cells and these arise during renal organogenesis.