The pathogenetic mechanisms of the blunted nocturnal fall in blood pressure, frequently observed in elderly patients with essential hypertension, are unclear. The aim of this study was to evaluate the autonomic nervous system in elderly dipper and non-dipper hypertensive subjects. The study group consisted of twelve non-dipper and twelve dipper hypertensive patients (mean age 77.7 and 73.8 years, respectively). Non-dippers were defined as subjects whose nocturnal fall in systolic blood pressure (SBP), evaluated by means of Ambulatory Blood Pressure Monitoring, was less than 10% of diurnal SBP. All the patients underwent the following cardiovascular tests to explore autonomic function: Tilt Table, Valsalva Maneuver, Deep Breathing, Cough. The tests were performed under standard conditions, and heart rate and blood pressure were continuously recorded. Valsalva ratio (VR), Expiration/Inspiration Ratio (E/IR) and Cough Test Ratio (CTR) were calculated. Mann Whitney's and chi 2 tests were used for comparison between groups. Relationships were assessed by univariate and multivariate analyses. Non-dipper hypertensive subjects showed significantly lower scores in VR (11.1 +/- 0.08 vs 1.28 +/- 0.14), E/IR (1.11 +/- 0.07 vs 1.21 +/- 0.10), and CTR (1.07 +/- 0.02 vs 1.15 +/- 0.07). During the tilt test, a significant decrease in SBP and a late increase in heart rate were observed in non-dippers. The day-night difference in SBP was significantly related to VR, CTR and maximal SBP drop during tilting. The findings confirm that non-dippers show an impairment in autonomic nervous drive, which is characterized mainly by decreased parasympathetic activity. These observations may explain the increase in cardiovascular risk in non-dippers.