Ksp-cadherin is a unique, tissue-specific member of the cadherin family of cell adhesion molecules that is expressed exclusively in tubular epithelial cells in the kidney and developing genitourinary (GU) tract. Transgenic mice carrying 3425 bp of the Ksp-cadherin 5' flanking region linked to a lacZ reporter gene express beta-galactosidase exclusively in the kidney, although the expression pattern is incomplete (Am J Physiol 277: F599-F610, 1999). To further define the region that mediates tissue-specific expression, transgenic mice carrying 1341 bp or 324 bp of the 5' flanking region linked to a green fluorescent protein (GFP) reporter gene were produced. Transgenic mice carrying 1341 bp of the 5' flanking region expressed GFP in all embryonic tissues that endogenously express Ksp-cadherin, including the ureteric bud, Wolffian duct, Müllerian duct, and developing tubules in the mesonephros and metanephros. In the adult kidney, GFP was highly expressed in thick ascending limbs of Henle's loops and collecting ducts and weakly expressed in proximal tubules and Bowman's capsules. Transgenic mice carrying 324 bp of the 5' flanking region exhibited expression exclusively in tubular epithelial cells in the developing kidney and GU tract. Immunoblot analysis showed that the expression of GFP was restricted to the kidney in adult mice. Taken together, these results demonstrate that 324 bp of the Ksp-cadherin 5' flanking region is sufficient to direct epithelial-specific expression in the developing kidney and GU tract. Transgenic mice that express GFP in the mesonephros, metanephros, ureteric bud, and sex ducts may be useful for cell lineage studies.