1. The release of arginine vasopressin (AVP) after an osmotic stimulus and head-up tilt was assessed in diabetic subjects with and without autonomic neuropathy
2. Six diabetic subjects with (DAN +ve) and five without (DAN − ve) evidence of autonomic neuropathy and five normal subjects were infused with 5% (w/v) NaCl at a rate of 0.05 ml min−1 kg−1 body weight for 120 min. Blood pressure, heart rate and plasma AVP were measured over this period
3. Seven DAN +ve, six DAN −ve and six normal subjects were tilted head-up to 45° for 120 min. Blood pressure, heart rate and plasma AVP were measured during the study
4. Infusion of 5% (w/v) NaCl produced appropriate rises in plasma osmolality and plasma AVP levels which did not differ between the three groups, confirming the normal osmotic release of AVP in the diabetic subjects
5. During head-up tilt, there were no differences in AVP responses between the three groups, despite a major hypotensive stimulus in the DAN + ve group
6. We conclude that osmotic release of AVP is normal in diabetes, but that cardiovascular release of AVP is impaired in diabetic subjects with cardiovascular reflex evidence of autonomic neuropathy, reflecting an afferent defect.