DNA sequences encoding kidney renin were localized to region p21----qter of human chromosome 1 by Southern blot analysis of mouse-human somatic cell hybrids with a cloned human renin DNA probe. The renin gene may be a member of a chromosome 1 linkage group which is conserved in mouse and man. Available evidence suggests this gene is present in one copy per haploid genome. Thus those renin-like molecules detected immunologically in tissues other than the kidney (such as brain, placenta, uterus, pituitary, vasculature, and adrenal) may be derived from this single gene. Since renin messenger RNA in human kidney is about 1550 nucleotides long, reported molecular weights in excess of 45,000 for circulating renin represent posttranslational or postsecretory modifications of the polypeptide.