Plasma levels of alpha-human atrial natriuretic peptide (hANP) were measured in 17 patients with primary hypertension (11 females, 6 males, aged 22-61; blood pressure systolic 154 +/- 7 mmHg, diastolic 92 +/- 4 mmHg) and in 9 normotensive controls (4 males, 5 females, aged 20-71; blood pressure systolic 117 +/- 4 mmHg, diastolic 76 +/- 2 mmHg) during unrestricted sodium diet, at the 4th day of a low sodium intake (40-60 mEq/day) and at the 6th day of sodium loading (280-320 mEq/day) both after an overnight rest and after 4 h of upright posture. In the controls, plasma levels of hANP at 8:00 a.m. were lowered from 73 +/- 11 to 49 +/- 7 pg/ml during low sodium diet and increased to 128 +/- 37 pg/ml after high salt intake. Plasma ANP levels were significantly lower after 4 h of upright posture during unrestricted, low and high sodium intake. In the hypertensive group, plasma ANP levels were elevated during unrestricted diet (203 +/- 43 pg/ml), during the low sodium period (139 +/- 31 pg/ml), and after high sodium intake (267 +/- 63 pg/ml) compared to the controls. All levels were lowered by upright posture. The absolute decrease was more pronounced compared to the normotensives, the relative decline was similar in both groups. In the hypertensives, plasma ANP levels significantly correlate with systolic and diastolic blood pressure (r = 0.468, r = 0.448, P less than 0.05) and with urinary aldosterone during unrestricted diet (r = 0.536, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)