In glomerular development, the glomerular epithelium is derived from the lower loop of the S-shaped renal vesicle. However, it is unclear whether the capillary endothelium is derived directly by vasculogenesis (e.g. differentiated directly from local metanephric mesenchyme) or whether they are derived by angiogenesis (i.e. derived from pre-existing vasculature in the metanephros). This question has been addressed in other laboratories using surgically created chimeric kidney model systems. In the present study, chimeric kidneys were developed by aggregating the cells from 4- to 8-cell embryos from Mus musculus with ones from Mus caroli and implanting the aggregated embryos into pseudopregnant hosts [Goldowitz D: Neuron 1989;3:705–713]. Species specific DNA clones were used in conjunction with in situ hybridization to identify the species origin of cells. Interspecies aggregate chimeras had varying proportions of renal cells derived from Mus caroli and Mus musculus; however, regions were identified in which the renal tubular and Bowman’s capsule or parietal epithelia were from one species while vessel endothelium and cells in the interstitium were from the other species. In those regions, glomeruli always contained an admixture of cells from both species however; many of the glomerular endothelial cells appear to be from the same species as the vessel endothelium and interstitial cells. These findings support the hypothesis that angiogenesis may contribute cells that help form the glomerular capillary endothelium. Most intrarenal arteries contained cells from both species. However a few vessels were found in which the endothelium was derived from one species while the smooth muscle cells were from the other species. This finding suggests that intrarenal arterial development has two cells of origin: the endothelial tube develops and is surrounded by mesenchymal cells that form the tunica media. The aggregation chimeric mouse kidney may become a useful model system for studying in situ aspects of the complex processes involved in kidney development.