Increased plasma norepinephrine levels have been observed in some persons with early essential hypertension. Although both plasma norepinephrine level and mean arterial blood pressure rise with age, little is known about the state of catecholamine secretion in elderly patients with essential hypertension. We studied the 24-hour cycle levels of plasma norepinephrine, epinephrine, and dopamine in 12 elderly hypertensive subjects and 13 age-matched normotensive controls (mean ages, 63.8 +/- 1.2 yr and 64.8 +/- 1.8 yr [SEM] respectively). Blood samples were obtained at bihourly intervals from 0900 to 2100 hours and every 30 minutes from 2100 to 0900 hours, during which time sleep and breathing were continuously monitored. A circadian rhythm was displayed in both groups by plasma epinephrine levels (mesor, 49 +/- 2 pg/ml and 38 +/- 1 pg/ml; amplitude, 15 +/- 2 pg/ml and 11 +/- 1 pg/ml; acrophase, 12.20 +/- 0.40 hr and 14.41 +/- 0.34 hr in the normotensive and hypertensive groups respectively) but not by plasma norepinephrine or dopamine levels. During the 24-hour cycle plasma epinephrine, but not norepinephrine or dopamine, levels were positively related to mean arterial blood pressure (r = 0.60 for the normotensive subjects, r = 0.57 for the hypertensive subjects, p less than 0.01 for both).(ABSTRACT TRUNCATED AT 250 WORDS)