It has been observed that a distinct blood pressure (BP) response to prolonged and forced hyperventilation in adult patients with essential hypertension is associated with significant changes in plasma catecholamine and β-endorphin levels. This paper investigated whether hemodynamic and neuro-endocrine responses to hyperventilation in elderly patients with essential hypertension (n = 39, mean age 81 ± 3 years) differ from those in elderly patients with secondary hypertension (isolated systolic hypertension, bilateral chronic nephropathy, nephroangiosclerosis, diabetic nephropathy and hyperparathyroidism) (n = 39, mean age 80 ± 1 years). Plasma β-endorphin levels were normal in patients with essential hypertension and increased in patients with secondary hypertension. Plasma norepinephrine levels were normal in both populations. Hyperventilation decreased BP and norepinephrine levels and increased β-endorphin levels in essential hypertensive patients, whereas it did not significantly change BP or neuro-hormonal levels in secondary hypertensive patients. Hierarchical cluster analysis based on BP response to hyperventilation disclosed a sub-group of essential hypertensive patients with the highest basal levels of norepinephrine and the lowest β-endorphin levels, in whom the BP decrease following hyperventilation was correlated with the decrease in norepinephrine and increase in β-endorphin levels. This suggests that b-endorphin may be involved in modulating sympatho-adrenergic activity in elderly patients with essential hypertension.