alpha-Lipoic acid is a very efficient antioxidants for the treatment and prevention of diabetic neuropathy. The aim of the present study was to evaluate the function of nitric oxide (NO) and stress proteins (HSP72) in insulin-dependent diabetes complicated by polyneuropathy and possible contribution of these systems to the therapeutic effects of alpha-lipoic acid. Plasma content of nitrites and nitrates in diabetic patients was almost 2-fold below the normal. The treatment with alpha-lipoic acid completely normalized the plasma content of these stable NO metabolites. The majority of patients had also low level of HSP72. Positive clinical effects of alpha-lipoic acid were accompanied by normalization of HSP72 synthesis. Thus, activation of the NO and HSP protective systems is involved in the therapeutic effect of alpha-lipoic acid in diabetic patients (type 1 diabetes mellitus) with polyneuropathy.