Atrial natriuretic peptide is shown to be a hormone having a certain part to play in the regulation of arterial blood pressure and water-salt metabolism. Results of study on the plasma content of the hormone in patients with various forms of arterial hypertension of endocrine genesis are presented. Differentially directed changes have been revealed in concentrations of immunoreactive atrial natriuretic peptide. Elucidation of the role of these in the pathogenesis of the pathology under consideration warrants further study in a comparative evaluation wtih the parameters of cardiohaemodynamics and water-salt metabolism.