Background: The kidney development involves a wide variety of developmental processes requiring a lot of genes expressed in a sequential manner. The aim of the present study is to identify new genes involved in these processes. Methods: To obtain a view of the mouse embryonic kidney transcriptome we used the SADE method, which allows large-scale quantitative gene expression measurements. Results: 7,689 tags were sequenced from our library. Among the 4,507 unique transcripts yielded, 64% correspond to known genes, 22% ESTs, 12% unidentified genes. 472 genes were differentially expressed as compared to published adult kidney library. Among these, we identified several candidate genes and focused on a particular one: thymosin β 4 ( Tβ 4), an actin-sequestering protein more highly expressed in fetal kidney. First we studied the in vivo expression patterns of Tβ 4 transcript during kidney development. Tβ4 increases throughout the kidney development and remains high during active nephrogenesis. Moreover, the spatial distribution of Tβ 4 mRNA was analysed and reveals that during active nephrogenesis (i.e., 18 dpc) Tβ 4 is localised in differentiating glomeruli. In adult kidney, Tβ4 remains expressed in podocytes and collecting ducts. Conclusion: Our results provide the first demonstration of Tβ4 production in vivo by embryonic kidney and further show that Tβ4 is implicated in kidney organogenesis.