A new mouse metanephric organ culture system has been developed to study mammalian renal development. The system permits in vitro organotypic differentiation in a serum-free, hormone supplemented medium consisting of Dulbecco's minimal essential medium (MEM) and Ham's F12 medium supplemented with insulin, 5 microgram/ml; PGE1, 25 ng/ml; T3, 3.2 pg/ml; hydrocortisone, 5 microgram/ml; and transferrin, 5 microgram/ml. In this system, metanephric development continues morphologically beyond the S-shaped tubule stage. A well differentiated proximal tubule forms with a well defined brush border, specialized intercellular connections, and an apical endocytic network. In addition, a unique devascularized glomerulus, with highly differentiated podocytes surrounding areas of basement membrane, forms entirely from epithelial elements. The present organ culture model goes beyond the limitations of previously described systems in that it does not require separation of nephrogenic blastema from ureteric bud, nor require animal serum or nonspecific tissue extracts for metanephric development. The model is thus suited for morphological, biochemical, and endocrinological study of normal and abnormal renal organogenesis.