Epithelial glomerular cells differentiate from mesenchymal cells of the metanephrogenic blastema. During the first stages of glomerulogenesis, the cells acquire the morphological features of epithelial cells. Then, podocytes lose these characteristics at the maturing glomerular stage. We have studied the molecules associated with junctional complexes during glomerular differentiation in human and pig fetal kidneys. We show for the first time the expression of P-cadherin in renal cells. Epithelial cells of ureteral buds and ampullae display all the molecules associated with junctional complexes and coexpress E- and P-cadherin. However, P-cadherin, plakoglobin and vinculin are the only markers detected in future glomerular cells. We have established a spatiotemporal correlation between the time of appearance and disappearance of junctional complexes as previously described (Saxén and Wartiovaara, Int. J. Cancer 1:271-290, 1966; Saxén et al., Adv. Morphog. 7:251-293, 1968; Reeves et al., Lab. Invest. 39:90-100, 1978), and the expression of their associated molecules. Epithelial cells with stable, typical junctional complexes strongly express the molecules associated with junctions, whereas cells endowed with transient, atypical junctional complexes express low amounts of components associated with junctions. These observations suggest a correlation between the level of expression of these components and an authentic, stable epithelial phenotype.