Activation of the renin-angiotensin system may in part be responsible for the abnormally increased vascular tone which occurs in heart failure; it has also been suggested that this system's responsiveness may diminish with age. We investigated the effects of posture and upright exercise on renin, angiotensin II, aldosterone and catecholamines in 8 patients over 65 years and in 10 patients under 65 years, all of whom had congestive heart failure. Samples were taken supine, after 5 min standing in the upright posture, and after exercise. Exercise time was similar between the two groups [5 X 3 +/- 1 X 9 min (mean +/- SD) in the younger group, compared with 5 X 2 +/- 3 X 4 min in the older group]. Resting renin and angiotensin II were similar and rose on standing with a further increase during exercise; there were no statistically significant differences between the groups. However, aldosterone rose during exercise only in the younger group, while increases in plasma noradrenaline were greater in the elderly. This study implies that the efficacy of angiotensin converting enzyme inhibitors is likely to be maintained in the elderly patient with heart failure.