Nadolol was effective and well tolerated as once-daily monotherapy for mild to moderate essential supine diastolic hypertension (SDBP) in 10 young (mean age, 39 years) and 12 elderly (mean age, 68 years) patients in a single-blind, placebo-baseline, escalating-dose study. Doses required to reduce SDBP to 90 mm Hg were not different in young (1.08 +/- 0.21 mg/kg/day) and elderly (0.82 +/- 0.14 mg/kg/day) patients (mean +/- SE). Trough plasma nadolol concentrations at steady state were similar and were linearly related to dose in both groups. More unchanged nadolol was recovered in 24-hour urine samples from young subjects (15.6% +/- 1.9%) than from elderly ones (10.7% +/- 1.1%) (p = 0.028). With increasing nadolol doses, plasma norepinephrine concentration increased and isoproterenol sensitivity decreased in both young and elderly subjects, and creatinine clearance and plasma active renin levels were unchanged; plasma inactive renin levels increased in the young, and aldosterone concentration declined in the elderly with the lowest nadolol dose.