Increased oxidative stress and advanced glycosylation are important factors in the development of diabetic neuropathy. In non-diabetic neuropathies their influence has not been investigated in detail so far. We studied the localisation of N ^ε-carboxymethyllysine (CML) – a biomarker for oxidative stress – by immunohistochemistry in sural nerve biopsies of 31 patients with different polyneuropathies [diabetic polyneuropathy (n=5), alcohol-associated polyneuropathy (n=4), vitamin B12-deficient polyneuropathy (n=6), chronic inflammatory demyelinating polyneuropathy (CIDP) (n=6), vasculitic neuropathy (n=6), Charcot-Marie-Tooth disease type I (CMT I) (n=4)] and 4 normal controls. CML was detected in the perineurium of patients with diabetic, alcohol-associated, vitamin B12-deficient and vasculitic polyneuropathies. Epineurial, perineurial and endoneurial vessels were CML positive in diabetic, vitamin B12-deficient and vasculitic polyneuropathies. CML was also found in mononuclear inflammatory cells in vasculitic neuropathy. In CIDP and normal controls there was only marginal perineurial CML deposition in 2/6 and 1/4 cases. In CMT I no CML was detected. Immunohistochemical results were confirmed by immunoblot. Our data suggest a role of oxidative stress in the pathogenesis not only of diabetic but also of alcohol-associated, vitamin B12-deficient and vasculitic polyneuropathies. It may be a minor pathogenetic factor in CIDP and may not be involved in CMT I. Underlying causes for increased oxidative stress may be an elevated production of reactive oxygen species and an impairment of antioxidative defences. Therefore, an antioxidative treatment should be considered in alcohol-associated, vitamin B12-deficient and vasculitic polyneuropathy.