Increased sympathetic nerve activity may play an important role in the pathogenesis of essential hypertension. It is well known that both dietary sodium intake and age influence the plasma norepinephrine (NE) concentration. The present study was undertaken to evaluate the effects of age on sympathetic nerve activity in patients with essential hypertension and normal control subjects under low-, regular-, and high-sodium regimens (mean 24-hour sodium excretions: 30 ± 4,116 ± 7, 280 ± 15 mEq, respectively). Plasma NE and eplnephrine (E) were analyzed by trihydroxyindole methods after high-performance liquid chromatography separation. Subjects were categorized by age into young (⩽40 yrs), middle-aged (40–60 years), and old (⩾60 years) subgroups. Mean plasma NE in hypertensive patients was significantly higher (p< 0.01) than in normal subjects on each of the sodium regimens. In normal control subjects, there was a significant positive correlation between age and plasma NE with all three sodium intakes. However, no correlation was seen in hypertensive patients on any of the sodium regimens, because in the young subgroup of hypertensive patients the mean plasma NE was significantly higher than that of normal control subjects. These results suggest that the increased sympathetic nerve activity plays an important role in the pathogenesis of essential hypertension, especially in young patients.