The effect of postural changes on plasma atrial natriuretic factor (ANF) levels was investigated in 16 diabetic hypertensives (eight with and eight without mild autonomic neuropathy) and in 10 hypertensives. The presence of renal damage or secondary hypertension was excluded. All diabetic patients were in good metabolic control. In upright position, the mean levels of plasma ANF were of 23.1 +/- 7.6 pg/mL in neuropathic diabetic hypertensives, 24.2 +/- 8.3 pg/mL in diabetic hypertensives, and 21.6 +/- 6.7 in essential hypertensives. Percentage decrease observed after the assumption of supine position was 47 +/- 18, 50 +/- 10, and 46 +/- 13, respectively. No significant difference was found between hypertensives and diabetic hypertensives, even in the presence of mild autonomic neuropathy. Plasma ANF response to postural changes was similar in all groups.