Abnormal patterns of diurnal blood pressure (BP) variation have been reported to be related to advanced target organ damage and poor cardiovascular prognosis. However, the neurohumoral characteristics of patients with such variation have not been fully investigated. We measured BP and plasma levels of neurohumoral factors (norepinephrine [NE], epinephrine, renin, and arginine vasopressin [VP]) during the 70 degree head-up tilt test (10 min supine and 15 min tilting) in 120 older subjects (mean age 71 years) who had sustained hypertension as determined by ambulatory BP monitoring. They who were subclassified according to the nocturnal systolic BP fall as follows: 28 extreme dippers with >20% nocturnal BP fall; 78 dippers with >0% but <20% fall; and 14 nondippers with <0% fall. Plasma renin activity (r = 0.22, P = .02) and VP level (r = 0.36, P < .0001) after tilting were positively associated with the nocturnal systolic BP fall. Plasma NE levels were significantly higher in nondippers than in dippers in both the supine and tilting positions (supine 519 v 315 pg/mL, P = .001; tilting 803 v 550 ng/mL, P < .01), whereas the increase of NE induced by tilting was comparable in the two groups. Plasma renin activity in both the supine and tilting positions was comparable in the three groups, but the increase of this activity caused by tilting was less marked in the nondippers than in the extreme dippers (0.05 v 0.26 ng/mL/min, P = .02) and dippers (0.21 ng/mL/min, P = .07). Plasma VP was markedly increased after tilting in the extreme dippers compared with dippers (3.8 v 2.6 pg/mL, P < .001) and nondippers (v 2.0 pg/mL, P < .001), whereas the levels in the supine position were comparable in the three groups (2.0 pg/mL for extreme dippers, 1.9 pg/mL for dippers, 1.6 pg/mL for nondippers). In conclusion, diurnal BP variation in elderly hypertensive individuals was significantly associated with neurohumoral factors regulating circulating blood volume. Increased VP after tilting in extreme dippers might counteract reduced circulating blood volume, whereas nondippers appear to have alpha- and beta-adrenergic subsensitivity that may be induced by their chronic exposure to high NE levels.