1. We studied 12 normotensive non-ketotic diabetic patients during poor metabolic control, with sustained hyperglycaemia, and again, after an interval of 3 weeks, when metabolic control was improved. On each occasion we measured blood pressure, total exchangeable sodium, plasma volume, transcapillary escape rate of albumin, and plasma concentrations of angiotensin II and aldosterone.
2. With improved diabetic control there was a small but significant fall in arterial pressure. Total exchangeable sodium was normal when control was poor but rose significantly to above normal with improved control.
3. Plasma volume also rose significantly with improved control, and the transcapillary escape rate of albumin fell and the intravascular mass of albumin rose.
4. Plasma angiotensin II and aldosterone concentrations were significantly above normal during poor metabolic control, but fell to normal with improved control.
5. These findings indicate a resetting of the relationship between blood pressure and exchangeable sodium when diabetic control improves. The association between exchangeable sodium and concentrations of angiotensin II and aldosterone also appears altered in diabetic patients. These changes associated with varying metabolic control must be considered when studying cardiovascular disease in diabetic patients.