The molecular basis of the organogenesis of the mammalian kidney is being investigated at multiple levels, with several exciting developments. Cellular signaling during and after kidney induction may be mediated in part by Wnt genes, which encode secreted, matrix-associated peptides. The Wilms' tumor suppressor gene WT1 is required for the kidney mesenchyme to respond to induction; the transcription factor Pax-2 may regulate the aggregation and proliferation of the kidney mesenchyme immediately after induction. Although the links between signaling molecules, their receptors, and the activation and repression of transcription factors in the kidney remain to be determined, several key elements of the genetic cascade driving kidney morphogenesis are now characterized.