Epidermal growth factor (EGF) stimulates the mitosis and differentiation of a variety of cellular types. It also delays the cell senescence in vitro. Because of its multiple functions, the effects of EGF on cells from isolated, explanted calf renal glomeruli have been studied. The cell types emerging from glomeruli cultured with and without EGF were compared and identified by morphological, immunofluorescence and electron microscopy criteria. Two cell types: visceral epithelial cells or podocytes (type I) and mesangial cells (type II) emerged from glomeruli cultivated without EGF. A third cell type, called type III cells, appeared only in the presence of EGF. These cells divided, were mobile and had prolonged lifespan in culture. They appeared pavement-like, and acquired progressively the morphological features and cytoskeletal components of type I cells. They also showed certain characteristics of podocytes in vivo. We suggest that type III epithelial-like cells are precursor cells of podocytes, that EGF triggers their emergence from glomeruli and their subsequent proliferation and differentiation in vitro. EGF also prolongs their lifetime in culture.