Mean arterial pressure, heart rate, plasma catecholamines, renin activity, and vasopressin changes induced by a 30-degree head-up tilt were studied before and during epidural anesthesia with bupivacaine in eight elderly patients (ages 58–82 yr). The tilt performed before epidural anesthesia did not modify mean arterial pressure, heart rate, plasma catecholamines, renin activity, and vasopressin at 5 and 15 min. During epidural anesthesia, the superior level of analgesia ranged from T4 to T10. Epidural anesthesia induced significant (P< 0.05) decreases from control values in mean arterial pressure and plasma norepinephrine (from 85 · 6 to 67 · 8 mmHg and from 600 · 108 to 307 · 77 pg/ml, respectively, mean ± SEM) without significant changes in heart rate, plasma epinephrine, renin activity, and vasopressin. However 5 and 15 min after tilt, significant decreases from pretilt values were measured in mean arterial pressure (from 67 · 8 to 57 · 6 and 55 · 6 mmHg, respectively) and in heart rate (from 70 · 8 to 63 · 7 and 62 · 7 beats/min). Simultaneously, an increase in plasma vasopressin (from 14.8 · 5.5 to 36.2 · 10.3 and 40.0 · 10.5 pg/ml) was recorded, whereas plasma norepinephrine and epinephrine remained unchanged. Posttilt plasma renin activity values at 5 and 15 min were increased significantly when compared with the preepidural values (2,752 · 1,168, 2,410 · 1,214 and 713 · 190 pg · ml−1· h−1, respectively). The authors conclude that during epidural anesthesia in elderly patients 1) the heart rate and the plasma catecholamines responses to hypotension induced by tilt are impaired, even if the level of analgesia is below T4; and 2) vasopressin and, to a lesser degree, the renin–angiotensin system may play important roles in the regulation of arterial pressure.