Recently it was shown that blood pressure (BP) in the elderly may decrease after a meal. The pathophysiologic mechanism of this phenomenon is unknown. It has been suggested that a failure of insulin-mediated sympathetic nervous system activation plays a role. To evaluate the role of endogenous insulin, the effects of oral glucose and oral fructose loading on BP, heart rate and norepinephrine levels were studied in 10 young normotensive volunteers (YN), 10 young hypertensive patients (YH), 10 elderly normotensive volunteers (EN) and 10 elderly hypertensive patients (EH). Fructose, 75 g/300 ml of water, elicited--in contrast to the same amount of glucose--only a small increase in insulin and glucose levels. After glucose loading, mean arterial BP decreased by 17 mm Hg in the EH group (p less than 0.001), 6 mm Hg in the EN group (p less than 0.01) and 7 mm Hg in the YH group (p less than 0.001), and did not change in the YN group. After oral fructose loading, BP did not change in any group. In all groups except the YN group, the increases in norepinephrine level and heart rate after both tests were not significantly different. These findings suggest that the BP reduction after glucose loading is related to glucose-mediated factors. A failure of insulin-mediated sympathetic nervous system activation does not appear to play a major role.