Plasma atrial natriuretic peptide (ANP) was measured in 717 subjects in a cross-sectional study of patients with hypertension (treated and untreated) and normotensive controls, representatives of a geographically defined population. ANP concentrations did not differ between the groups and there was no correlation with blood pressure. These results do not support the view that hypertensive and normotensive subjects have different ANP concentrations; they also call into question the role of ANP in the development of high blood pressure.