Adrenomedullin (AM) is a hypotensive peptide widely produced in the cardiovascular organs and tissues. We have cloned and sequenced the genomic DNA encoding the human AM gene and have determined that the gene is located in the short arm of chromosome 11. The 3′-end of the gene is flanked by the microsatellite marker of cytosine adenine (CA) repeats. In this study, we investigated the association between DNA variations in AM gene and the predisposition to hypertension. Genomic DNA was obtained from 272 healthy normotensive subjects (NT) age 57±5 years and 266 patients with essential hypertension (EH) age 53±11 years. The DNA was subject to PCR using a fluorescence-labeled primer, and the number of CA repeats were determined by poly-acrylamide gel electrophoresis. The averaged blood pressure was 117±13/73±9 mm Hg in NT and 170±23/104±12 mm Hg in EH. In Japanese, there existed 4 types of alleles with different CA-repeat numbers: 11, 13, 14, and 19. The frequencies of these alleles were significantly different between NT and EH (χ²=9.43, P=0.024). Namely, 13.5% of EH carried the 19-repeat allele, whereas the frequency was 6.2% in NT (χ²=7.62, P=0.007). In NT, plasma AM concentrations were not significantly different between the genotypes. In conclusion, microsatellite DNA polymorphism of AM gene may be associated with the genetic predisposition to EH, although the gene expression is not likely to be affected by the genotypes.