NATHAN 2 is a randomized, placebo controlled, double blind multicenter trial with two parallel groups. The patient population to be studied are those with symptomatic diabetic polyneuropathy Stage 2. Treatment will consist of daily IV administration of 600mg of thioctic acid or placebo solution five days per week for three consecutive weeks. The objective of the study is assessment of symptom relief after parenteral treatment with thioctic acid and the primary endpoint measured will be the Total Symptom Score (TSS) feet.