To gain insight into the later stages of nephrogenesis, we detected the alterations in gene expression in rat kidney at two postnatal stages, P0 (O day after birth), the time at which nephrogensis is still active, and P21 (21 days after birth),when nephrogenesis is complete. Methods Sprague Dawley rats were mated. Kidneys were dissected from embryos at E15, El7,and E19, and from postnatal days P0, P7, P21, and adult rats. Suppression subtractive hybridization (SSH) analysis was performedand highly expressed genes were evaluated as molecular markers by real-time reverse transcription--polymerase chain reaction(RT-PCR), in sitn hybridization, and Western Blot. Results Several differentially expressed genes were identified, includingrPEA3, a member of the PEA3 subfamily of Ets domain transcription factors. Real time RT-PCR analysis revealed that rPEA3 exhibited dynamic developmental regulation, with high levels of expression from embryonic day E15 until birth, and declining levelsthereafter. By in sire hybridization, rPEA3 mRNA was detected in the ureteric bud (UB) and surrounding metanephric mesenchymeof the kidneys from El5 until birth, but was undetectable in mature kidneys. Conclusions These studies provide compellingevidence that the newly identified gene rPEA3 may play an important role in kidney development and differentiation.