Previous studies have shown reduced levels and total urinary excretion of prostaglandin E2 in a heterogeneous population of patients with hypertension. The following study was undertaken to extend these observations to focus on the influence of age and blood pressure on renal prostaglandin E2 excretion in males. Four groups of human subjects were studied on an ad libitum diet of at least 2 g salt per day: group 1 consisted of normal young men; group 2 consisted of young men with essential hypertension; group 3 consisted of older nonhypertensive men; group 4 consisted of older hypertensive men. Reduced urinary prostaglandin E2 excretion was seen in the elderly hypertensive group but not the young hypertensives. Thus, when all hypertensives were compared to control the reduced prostaglandin E2 excretion was accounted for primarily by the elderly hypertensives. The reduction of prostaglandin E2 excretion could not be accounted for by normal ageing alone. Whether cause or effect, alterations of renal prostaglandin physiology accompanied hypertension in elderly men. No clear alteration of prostaglandin E2 physiology was noted in young male hypertensives.