OVE26 mice are a transgenic model of severe early-onset type 1 diabetes. These mice develop diabetes within the first weeks of life and can survive well over a year with no insulin treatment, and they maintain near normal body weight. To determine whether OVE26 mice provide a valuable model of chronic diabetic nephropathy (DN), OVE26 diabetic mice were compared with their nondiabetic littermates for functional and structural characteristics of DN. OVE26 mice exhibited pronounced polyuria and significant albuminuria by 2 months of age (305 microg/24 h in OVE26 vs. 20 microg/24 h in controls). Albumin excretion rate increased progressively with age and exceeded 15,000 microg/24 h at 9 months of age. The profound loss of albumin led to hypoalbuminemia in some diabetic animals. Albuminuria coincided with an elevation in blood pressure as measured by tail cuff. The glomerular filtration rate (GFR) in OVE26 mice measured using fluorescein isothiocynate inulin clearance demonstrated that GFR increased significantly from 2 to 3 months of age and then decreased significantly from 5 to 9 months. GFR in 9-month-old diabetic mice was significantly lower than that of 9-month-old control mice. The decline in GFR coincided with a significant increase in renal vascular resistance. Structural studies showed an almost twofold increase in kidney weight between 2 and 5 months. Diabetic mice also showed progressively enlarged glomeruli and expanded mesangium with diffuse and nodular expansion of mesangial matrix. Tubulointerstitial fibrosis was also observed in these mice. Glomerular basement membrane was thickened in OVE26 mice. In summary, OVE26 mice demonstrate that most of the characteristics of human DN can be produced by chronic hyperglycemia in a murine model. This model will be useful for improved understanding and treatment of DN.