Background:There is evidence for an altered endothelial function in established hypertension but little is known about endothelial function in borderline hypertension. It has also been suggested that the early stages of hypertension are characterized by an increased sympathetic drive.Objective:To investigate whether alterations in endothelin, neuropeptide Y (NPY) and calcitonin gene-related peptide (CGRP) are already present in the borderline hypertensive stage.Design:A case-control study of age-matched men recruited from a population screening programme.Methods:Seventy-five men with stable borderline hypertension [diastolic blood pressure (DBP), 85–94 mmHg] and 75 age- and sex-matched normotensive controls (DBP ±80 mmHg) were investigated. Plasma samples were drawn in a standardized fashion, and extracted and analysed using competitive radio immunoassays.Results:Basal concentrations of NPY and CGRP were similar in the two groups (28.4 versus 26.7 pmol/l and 24.2 versus 21.7 pmol/l, respectively). Basal concentrations of endothelin were significantly higher in the borderline hypertensive group (2.0 versus 1.5 pmol/l,P<0.0001).Conclusions:These results suggest that a disturbed endothelial function, represented by endothelin, could be involved in the early hypertensive processes. They also suggest that these changes could be present before the basal sympathetic/parasym-pathetic drive alters, warranting further research into this area.