We recently reported the structure and functional expression of a human V1a vasopressin receptor (V1aR) cDNA isolated from human liver cDNA libraries. To understand further the expression and regulation of the V1aR, we now describe the genomic characteristics, tissue expression, chromosomal localization, and regional mapping of the human V1aR gene, AVPR1A. Tissue distribution of the human V1aR mRNA explored by Northern blot analysis of various human tissues or organs revealed the presence of a 5.5-kb mRNA transcript expressed in the liver and to a lesser degree in the heart, the kidney, and skeletal muscle. Screening of human genomic libraries revealed that the human AVPR1A gene is included entirely within a 6.4-kb EcoRI fragment and comprises two coding exons separated by a 2.2-kb intron located before the corresponding seventh transmembrane domain of the receptor sequence. The first exon also contains 2 kb of 5'-untranslated region, and the second exon includes 1 kb of 3'-untranslated region. 5'-RACE analysis of human liver mRNA by PCR localized the V1aR mRNA transcription start site 1973 bp upstream of the translation initiation site. Specific oligonucleotides derived from the intron sequence were used as primers in polymerase chain reaction (PCR) analysis of human/rodent somatic cell hybrids. AVPR1A was localized by PCR analysis of a somatic cell hybrid panel to chromosome 12. Fluorescence in situ hybridization using a yeast artificial chromosome physically mapped AVPR1A to region 12q14-q15.