Serial changes in the plasma hANP (human atrial natriuretic peptide) level in patients with essential hypertension were determined during high salt intake for two weeks after salt restriction for 5 days. The mean plasma hANP level decreased during salt depletion for 5 days from 60 +/- 10 pg/ml to 39 +/- 8 pg/ml. During high salt intake (20 g NaCl/day) for two weeks, the plasma hANP level increased gradually to a maximum of 71 +/- 16 pg/ml on day 7 and then decreased to 54 +/- 9 pg/ml on day 14. The plasma levels of renin activity, aldosterone and noradrenaline decreased during salt repletion. Changes in the plasma hANP level were correlated positively with those of urinary sodium excretion and negatively with those of plasma renin activity on days 7 and 14 of salt repletion. Change in the plasma hANP level correlated with that in the mean blood pressure on day 14, but not day 7 of salt repletion. These findings indicate that the plasma hANP level is closely related to sodium intake in patients with essential hypertension.