We studied the immunohistochemical localization of advanced glycosylation end products (AGEs) in the progression of diabetic nephropathy. Fourteen NIDDM patients with diabetic nephropathy were evaluated: 2 patients with normoalbuminuria, 4 with microalbuminuria (MA) and 8 with overt proteinuria (OP). Three patients with minor glomerular abnormalities were used as nondiabetic controls. Immunoreactivity to a monoclonal anti-AGE antibody (6D12) was recognized on the internal elastic membranes of arterial walls in every diabetic group. Hyaline lesions of arterioles of the MA and OP groups demonstrated strong reactions with 6D12. A portion of the nodular and exudative lesions in glomeruli of OP group patients also revealed immunoreactivity to 6D12. No immunoreactivity to 6D12 was observed in nondiabetic control specimens. We confirm that the accumulation of AGEs began in arterial walls of the early stage and presented in glomerular lesions of the late stage of the progression of diabetic nephropathy.