Anti-oxidant treatment has been shown to prevent nerve dysfunction in experimental diabetes mellitus, thus providing a rationale of potential therapeutic value for diabetic patients. The effects of the anti-oxidant -lipoic acid (thioctic acid) were studied in a 3-week multicentre, randomized, double-blind placebo-controlled trial (Alpha-Lipoic Acid in Diabetic Neuropathy; ALADIN) in 328 non-insulin-dependent diabetic patients with symptomatic peripheral neuropathy who were randomly assigned to treatment with intravenous infusion of -lipoic acid using three doses (1200, 600, or 100 mg ALA) or placebo (PLAC). Neuropathic symptoms (pain, burning, paraesthesiae, and numbness) were scored at baseline and at each visit (days 2–5, 8–12, and 15–19) prior to infusion. In addition, the Hamburg Pain Adjective List, a multidimensional specific pain questionnaire, and the Neuropathy Symptom and Disability Scores were assessed at baseline and day 19. According to the protocol 260 (65/63/66/66) patients completed the study. The total symptom score in the feet decreased from baseline to day 19 by –4.5±3.7 (–58.6%) points (mean ± SD) in ALA 1200, –5.0±4.1 (–63.5%) points in ALA 600, –3.3±2.8 (–43.2%) points in ALA 100, and –2.6±3.2 (–38.4%) points in PLAC (ALA 1200 vs PLAC: p=0.003; ALA 600 vs PLAC: p<0.001). The response rates after 19 days, defined as an improvement in the total symptom score of at least 30%, were 70.8% in ALA 1200, 82.5% in ALA 600, 65.2% in ALA 100, and 57.6% in PLAC (ALA 600 vs PLAC; p=0.002). The total scale of the Pain Adjective List was significantly reduced in ALA 1200 and ALA 600 as compared with PLAC after 19 days (both p<0.01). The rates of adverse events were 32.6% in ALA 1200, 18.2% in ALA 600, 13.6% in ALA 100, and 20.7% in PLAC. These findings substantiate that intravenous treatment with -lipoic acid using a dose of 600 mg/day over 3 weeks is superior to placebo in reducing symptoms of diabetic peripheral neuropathy, without causing significant adverse reactions.