An impaired synthesis of prostacyclin has been implicated in the development of essential hypertension (EH). We therefore investigated whether there is an association between the prostacyclin synthase (PGIS) gene and EH using a variable number of tandem repeats (VNTR) polymorphism in the promoter region that influences transcriptional activity of this gene. A total of 125 patients with EH and 125 age-matched subjects with normal blood pressure were studied. The number of VNTR of the five alleles ranged from 3 to 7 repeats in the 250 unrelated Japanese subjects. The allele frequency distribution in the two groups were not significantly different. Thus, this VNTR polymorphism in the PGIS gene is not associated with EH.