The aim of this study was to clarify the influence of hyperglycemia on the deposition of aggregated protein in the glomeruli of diabetic mice. KK-A(y) mice injected with aggregated bovine serum albumin accumulated more of it in the glomeruli than did ICR mice. There were no histological alterations in the glomeruli of KK-A(y) mice. KK-A(y) mice given voglibose in mouse-chow for 2 weeks had significantly reduced blood glucose, glycated albumin, and hemoglobin A(1C) levels compared with control mice. The voglibose-treated KK-A(y) mice were injected with aggregated bovine serum albumin and accumulated significantly less albumin in the glomeruli than did the control mice. Pioglitazone decreased blood glucose levels compared with the control, and reduced the glomerular deposition of aggregated albumin. Glomerular aggregated bovine serum albumin levels and blood glucose levels were reduced significantly by the injection of insulin. Six times more advanced glycation endproducts were produced from aggregated bovine albumin than from non-aggregated bovine albumin on incubation with glucose and L-lysine in vitro. Glucose-loaded ICR mice generated more advanced glycation endproducts from aggregated albumin, and had more aggregated bovine albumin in the glomeruli. It was suggested that hyperglycemia contributes to an increase in the deposition of aggregated protein in glomeruli even early on in diabetes.