Increased oxidative stress and subsequent activation of the transcription factor NF-kB has been linked to the development of late diabetic complications. To determine whether oxidative stress dependent NF-kB activation is evident in patients with diabetic nephropathy we used an Electrophoretic Mobility Shift Assay based semiquantitative detection system which enabled us to determine NF-kB activation in ex vivo isolated peripheral blood mononuclear cells. We examined 33 patients with diabetes mellitus (Type I and Type II). Patients with diabetic nephropathy showed higher NF-kB binding activity in Electrophoretic Mobility Shift Assays and stronger immunohistological staining for activated NF-kBp65 than patients without renal complications. NF-kB binding activity correlated with the degree of albuminuria (r = 0.316) and with thrombomodulin plasma concentrations (r = 0.33), indicative for albuminuria associated endothelial dysfunction. In a 3 day intervention study in which 600 mg of the antioxidant thioctic acid (α-lipoic acid) per day were given to nine patients with diabetic nephropathy oxidative stress in plasma samples was decreased by 48 % and NF-kB binding activity in ex vivo isolated peripheral blood mononuclear cells by 38 %.