Atrial natriuretic peptide-like immunoreactivity in plasma (ANP-LI) was studied in patients with severe hypertension (n = 21) and in matched healthy control subjects. There was no correlation between ANP-LI and blood pressure, and the distribution of ANP-LI values did not differ between the two groups. These results are consistent with the assumption that an increase in ANP is not caused by elevated blood pressure, although elevated ANP-LI may be found in subgroups of hypertensive subjects with increased atrial pressures due to, for example, cardiac failure.