To investigate the role of glucose and insulin in the development of hypotension following glucose ingestion in elderly subjects with orthostatic hypotension, the autonomic responses to glucose and xylose ingestion were studied in five elderly subjects with age related orthostatic hypotension (without autonomic failure), five elderly control subjects and three elderly subjects with evidence of autonomic failure. Heart rate, blood pressure, plasma noradrenaline and plasma arginine vasopressin responses to glucose ingestion and to xylose ingestion were investigated. All subjects were supine for 90 min following ingestion of each carbohydrate and were then tilted 45 degrees head-up for 10 min. Blood pressure was maintained in elderly control subjects following ingestion of both carbohydrates and during tilting. The elderly group with orthostatic hypotension, while supine had a fall in systolic blood pressure 60-90 min following both glucose and xylose ingestion. Diastolic blood pressure was lowered 60-90 min after glucose but not xylose. During tilting, blood pressure fell by similar levels following both carbohydrate ingestions; plasma noradrenaline levels after 2 min and plasma arginine vasopressin levels after 10 min tilting were significantly less following glucose ingestion compared to xylose ingestion. The autonomic failure group while supine had a fall in systolic blood pressure 60-90 min following both glucose and xylose ingestion. Diastolic blood pressure was lowered 60-90 min after glucose but not xylose. During tilting, blood pressure fell by similar levels following both carbohydrate ingestion. Plasma noradrenaline and arginine vasopressin levels were unchanged after ingestion of either carbohydrate, and during tilting.(ABSTRACT TRUNCATED AT 250 WORDS)