INTRODUCTION The aim of the work was to study the maintenance of atrial and brain natriuretic peptide (ANP, BNP) and endothelin-1 (ET-1) in patients with idiopathic arterial hypertension and the relationships between cardiac morphological parameters and concentrations of examined peptides in group of patients with left ventricular hypertrophy (LVH). METHODS Seventy-six patients were enrolled in the study: 21 patients with confirmed idiopathic arterial hypertension (group 1), 18 with idiopathic hypertension and eccentric hypertrophy (group 1a), 14 with idiopathic hypertension and concentric hypertrophy (group 1b), and 23 patients without arterial hypertension, organic heart disease, or chronic respiratory tract diseases (group 2 - control group). All subjects were submitted for echocardiographic evaluation. Posterior wall thickness (PWT), interventricular septum thickness (IVST), left ventricular end-diastolic diameter (LVEDd), left atrium diameter (LAD), left ventricular mass index (LVMI), ejection fraction (EF), fractional shortening (FS), midwall shortening fraction (MWS), and relative wall thickness index (RWT) were studied. Concentrations of ANP(1-28), BNP, and ET-1 were determined with the use of radioimmunological kits (RIA). The obtained results were subjected to statistical analysis. RESULTS A considerable increase of ANP and BNP was observed in all patients with hypertension (group 1) in comparison to patients without hypertension (group 2). Significant increases of ANP were found in groups 1a and 1b in comparison to group 1 and 2, as well as considerably increase of BNP in group 1b compared to groups 1, 1a, and 2. In the group of patients with hypertension (group 1), a significant increase in the concentration of ET-1 compared to group 2 was found. However, the concentrations of ET-1 in groups 1 and 2 were not statistically different. Significant differences in concentrations of ET-1 between groups 1a, 1b, and 1 and 2 were seen. Significant correlations were found between concentrations of ANP, BNP, ET-1 and morphological parameters: PWT, IVST, LVMI and RWT. In group 1b, a correlation between concentrations of ANP, BNP, MWS, and LAD was found. The multiple regression analysis showed that RWT independently correlates with concentrations of ANP and BNP, and the concentration of BNP is in closer relation to RWT than ANP. In the case of ET-1, the multiple regression analysis did not show that LVMI or RWT had any independent influence on secretion of ET-1 in patients with idiopathic hypertension and LVH. CONCLUSIONS Increased concentration of ANP in patients with idiopathic hypertension may point to the coexistence of complications with type of LVH. High concentration of BNP may specifically suggest concentric LVH. This is important - especially if there are difficulties in interpretations of results of other clinical examinations. However, increased concentrations of ET-1 in the plasma of patients with hypertension and LVH should not be treated as an indicator of LVH degree.