Data from gene ablation studies in mice have indicated critical roles for Lim-1, Wnt4, WT-1, and Pax-2 in the coordination and execution of kidney patterning and differentiation. However, the precise roles of these molecules, their ordering within a genetic hierarchy, and the manner in which they contribute to establishing the fates of cells of each of the components of the nephron have yet to be elucidated in any system. In this report, the temporal and spatial expression patterns of these genes within the Xenopus pronephric system were examined in detail by single- and double-probe in situ hybridization. We describe restrictions of these gene expression patterns within the pronephros which indicate a model for the partitioning of the common pronephric anlage into its three component parts--the tubules, the glomus, and the duct.