Background: Available evidence has shown that endothelin-1 (ET-1) acts in an autocrine/paracrine fashion rather than as a hormone or cytokine. Therefore, the analysis of local ET-1 production is a crucial step toward understanding its physiological and pathophysiological importance. In this study, in situ RT-PCR was utilized to detect tubular expression of prepro-ET-1 mRNA in normal rat kidney. Methods: Kidneys were taken from normal Sprague-Dawley rats weighing approximately 200 g. In situ RT-PCR was carried out using the preparations embedded in paraffin and cut at a thickness of 8 µm. Furthermore, we tried semiquantitation of the prepro-ET-1 mRNA expression along different nephron segments by densitometric analysis. Results: Prepro-ET-1 mRNA expression was detected in all tubular segments of the kidney from normal rats. Densitometric analysis demonstrated its highest expression in cortical collecting duct (CCD) and outer medullary collecting duct (OMCD). The expression was the lowest in thin descending limb of Henle’s loop (TDL). Conclusion: This study showed that all tubular segments have the ability to synthesize ET-1 in rat kidney. It would be worth evaluating the levels prepro-ET-1 mRNA expression in various diseases by in situ RT-PCR to understand its pathophysiological role in such settings.