BACKGROUND Endothelin-1 (ET-1) may play an important role in the development and maintenance of hypertensive states. In patients with essential hypertension, ET-1 plasma concentration increases or remains unchanged. The aim of the present study was to investigate ET-1 plasma concentration in patients with mild-to-moderate essential hypertension and its interrelationship with catecholamines, neuropeptide Y and atrial natriuretic peptide (ANP). METHODS The study included 37 patients (mean age 38.2 +/- 1.6 years) with mild-to-moderate essential hypertension. The control group consisted of 21 healthy volunteers (mean age 35.6 +/- 1.4 years). ET-1, neuropeptide Y and ANP were determined by radioimmunoassay methods and catecholamine plasma concentration was determined radioenzymatically. RESULTS Our study shows that plasma ET-1 and neuropeptide Y levels are elevated in patients with essential hypertension compared with a control group. No correlation was found in either of the groups between plasma ET-1 level and plasma neuropeptide Y, catecholamine or ANP concentrations. CONCLUSIONS Our results suggest that ET-1 is relevant in the development and maintenance of elevated blood pressure.