Relatively few data exist on atrial natriuretic peptide (ANP) characteristics in Type 2 diabetes mellitus (DM). Therefore, plasma immunoreactive ANP concentrations were measured before and for 4 h following the ingestion of a physiological mixed meal in 8 newly diagnosed, normotensive, normoalbuminuric, patients with Type 2 DM and 6 normotensive, non-diabetic controls. In patients with Type 2 DM, basal plasma ANP concentrations were 4.0 +/- 2.0 and not significantly changed following ingestion of the meal, with peak levels of 4.9 +/- 2.8 pmol l(-1). Non-diabetic controls had higher basal plasma ANP concentrations, 8.7 +/- 3.4 pmol l(-1) (p < 0.05), significantly increasing to a peak of 11.9 +/- 6.3 pmol l(-1) at 30 min post meal. Extracellular fluid volume (ECV) was not different between diabetic patients and controls (15877 +/- 2679 vs 13668 +/- 1792 ml3). Glomerular filtration rate (GFR) (isotopic clearance corrected for body surface area) was elevated in diabetic patients (mean +/- SD) 130 +/- 39 vs 98 +/- 10 ml min(-1), p < 0.05). For the DM subjects, basal ANP levels were negatively correlated with GFR (rs - 0.74, p < 0.05) and effective renal plasma flow (ERPF) (rs - 0.8, p < 0.05). We conclude that patients with Type 2 DM demonstrate reduced basal plasma ANP concentrations which are inversely correlated to renal function. In contrast to non-diabetic controls, ANP in Type 2 DM does not rise in response to feeding.