A deficient dopamine D(2) receptor (DA2) formation or action may contribute to hypertension via an increase of catecholamine release. In addition, Axis II personality disorders that appears odd or eccentric (cluster A) is associated with a low density of DA2. This study sought to examine if a NcoI restriction fragment length polymorphism (C to T transition) in exon 6 of the dopamine D(2) receptor gene (DRD2) was associated with these characteristics. The genotypes (CC, CT and TT) were compared in anthropometric, endocrine, metabolic and haemodynamic variables as well as estimates of personality disorders in 284 randomly selected 51-year-old men. Homozygotes for the C allele constituted 49% of the men and homozygotes for the T allele 9%, while heterozygotes were 41%. The TT genotype was associated with elevated systolic and diastolic blood pressure, independent of obesity and endocrine abnormalities, including the hypothalamic-pituitary-adrenal axis regulation. Moreover, the TT genotype was significantly more frequent among subjects with grade 1 (mild) hypertension (>140/90 mm Hg) compared to normotensive subjects (<130/85 mm Hg). The polymorphism in exon 6 of the DRD2 was also significantly associated with cluster A personality disorders. These results suggest that a polymorphism in exon 6 of the DRD2examined with the restriction enzyme NcoI is associated with an elevated blood pressure, independent of obesity. Paranoid or schizoid personality disorders is also associated with a polymorphism of the DRD2, which might be associated with a previously demonstrated low density of this receptor.