To date, many mutations, including intronic nucleotide changes, in the SLC12A3 gene encoding the thiazide-sensitive sodium-chloride cotransporter (NCCT) have been reported in Gitelman's syndrome (GS) patients. However, it has not been clarified whether intronic nucleotide changes affect mRNA content. Since mRNA analysis is possible only after obtaining renal biopsy specimens, no studies have been conducted to identify transcript abnormalities in GS. In the study reported here, we investigated such transcript abnormalities for the first time by using mRNA expressed in a patient's urinary sediment cells. Direct sequencing analysis of leukocyte DNA disclosed one known missense mutation (R399C) and one known nucleotide change of the splicing acceptor site of intron 13 (1670-1 g > t). mRNA extracted from the urinary sediment cells was analyzed by RT-PCR to determine the pathogenic role of the intron mutation. A fragment encompassing exon 13 to 15 was amplified as two products, one consisting of all three exons and the other lacking only exon 14 in its entirety. Our investigation was the first to demonstrate exon 14 skipping in an NCCT transcript in renal cells. This methodology thus constitutes a potential noninvasive analytical tool for every inherited kidney disease.