Aim of this study was to verify the existence of a correlation between the insular hormones and the atrial natriuretic factor (ANF). We studied 70 subjects (20 control, 20 obese, 20 non insulin-dependent diabetic obese, 10 insulin-dependent diabetic subjects) submitted to a glucagon test (1 mg i.v.). Blood samples were collected at -15, 0, 3, 6, 12, 15, 30, 60, 120, 150 minutes to assay insulin, C-peptide, serum electrolytes and ANF levels. The results to point out are: the ANF basal values are significantly higher (p < 0.01) in non insulin-dependent obese patients than in controls; the obese subjects also present a significant difference (p < 0.05). After glucagon injection no variations have been found in the ANF values until the 15th minute; then the controls, the obese and, above all, the non insulin-dependent diabetic obese subjects showed a significant increase of the ANF values between 60' and 90' (basal values 38 +/- 4 ng/ml; 90' values 85 +/- 7 ng ml). As these high values appear only after the induction of hyperinsulinism in our experiment and are not present in the type-1 diabetic subjects, it's probable that insulin, rather than glucagon, stimulates, directly or indirectly, the ANF secretion. If this hypothesis is confirmed, the correlation between insulin and ANF should deserve attention from a therapeutic point of view in subjects with glycometabolic imbalance.