The epithelial Ca2+ channel, ECaC, represents the rate-limiting step of vitamin D-3-regulated Ca2+ (re)absorption in kidney and intestine, and provides, therefore, a new candidate gene for Ca2+-related disorders. To supply the basis for direct mutation analysis, we report here the structure of the human ECaC gene (ECAC1(2)). It consists of 16 exons spanning 25 kb with introns ranging from 98 to 8500 bp. The 5'-flanking region of ECAC1 contains four putative vitamin D(3-)responsive elements. At positions -92 and -13 transcription initiation sites were identified, but the former lacks the canonical TATA or CAAT boxes. ECAC1 was mapped to chromosome 7q35 by fluorescent in situ hybridization, reassigning a previous radiation hybrid mapping to 7q31.1-2. The gene of a recently identified rat intestine homologue of ECaC, named Ca2+ transporter 1, was found juxtaposed to the ECaC gene, indicating that both genes are the products of evolutionary local gene duplication.