The effect of alloxan monohydrate-induced diabetes on the resting plasma atrial natriuretic peptide (ANP) level was investigated in 22 male New Zealand white rabbits. Alloxan monohydrate (100 mg/kg) dissolved in saline at a concentration of 50 mg/ml was administered by a single intravenous injection 3 months before the experimental analysis. The diabetic state was examined 72 h later by quantitative determination of blood glucose levels of >350 mg/dl. Beginning on day 3, 14 animals (Group 1) received a daily subcutaneous injection of 1 U insulin having moderate hyperglycemia (blood glucose concentration [BGC] between 300 and 400 mg/dl). Eight animals (Group 2; normoglycemic controls) received 3.2 U of insulin daily to maintain the BGC below 100 mg/dl. Eight healthy rabbits were included in the study as controls (Group 3). Blood samples for ANP analysis were obtained three months after administration of alloxan monohydrate.