Evaluation of thick ascending limb (TAL) function has been hindered by the limited ability to selectively examine the function of this nephron segment in vivo. To address this, a Cre/loxP strategy was employed whereby the Tamm-Horsfall (THP) promoter was used to drive Cre recombinase expression in transgenic mice. The THP gene was cloned from a mouse genomic library, and 3.7 kb of the mouse THP 5'-flanking region containing the first noncoding exon of the THP gene were inserted upstream of an epitope-tagged Cre recombinase (THP-CreTag). THP-CreTag transgenic mice were bred with ROSA26-enhanced yellow fluorescent protein (eYFP) mice (contain a loxP-flanked "STOP" sequence 5' to eYFP), and doubly heterozygous offspring were analyzed. THP and eYFP were expressed in an identical pattern with predominant localization to the renal outer medulla without expression in nonrenal tissues. eYFP did not colocalize with thiazide-sensitive cotransporter (distal tubule) or neuronal nitric oxide synthase (macula densa) expression. THP mRNA expression was detected only in kidney, whereas CreTag mRNA was also present in testes. These data indicate that THP-CreTag transgenic mice can be used for TAL-specific gene recombination in the kidney.