Development of the different renal capillary beds requires that the transformation of the metanephrogenic mesenchyme and ureteric bud into the different nephron segments be temporally and spatially coordinated with the migration and growth of the endothelial cells present in the renal anlage. This suggests that ureteric bud and/or metanephrogenic mesenchymal cells provide molecules which guide endothelial cells to their appropriate locations. We found that monoclonal antibody (MAb) 5B6-E4, obtained with mechanically dispersed cells of embryonic day 15 (E15) rat renal anlage, identifies an antigen that is temporally and spatially associated with endothelial cell location and migration during renal development. Furthermore, 5B6-E4 disrupts the close association between ureteric bud ampullae and endothelial cells in E14 renal anlages grown in vitro: whereas 43% of the ureteric bud ampullae were in contact with endothelial cells in control conditions, the presence of 20 microg/ml 5B6-E4 reduced this number to 22% (P < 0.02). These results suggest that the antigen recognized by 5B6-E4 is involved in endothelial cell targeting during renal development.