Fidarestat (SNK-860) is an aldose reductase inhibitor codeveloped by Sanwa Kagaku, NK Curex, and Sankyo for the treatment of distal symmetric polyneuropathy (DSP). In a Phase III trial, 279 patients with DSP were randomized to receive fidarestat (1 mg daily) or placebo for 52 weeks. Evaluation of efficacy was based on changes in clinical symptoms (numbness, pain, rigidity, alterations in temperature perception, paresthesia, hypesthesia, and weakness) as well as changes in electrophysiological measurements such as F-wave NCV. Five of six electrophysiological measures assessing function in motor nerves showed statistically significant improvement from baseline within the treatment group; a comparison of the placebo and treatment groups on these measures, however, showed the statistical difference on only two of the six measures. Two electrophysiological measures of sensory function failed to show a statistically significant difference from baseline in the fidarestat group. Statistically significant improvements over placebo were noted on several measures of subjective symptoms (e.g., numbness of upper extremities, decreased tactile sensitivity in lower extremities, paresthesia in the sole), with a greater divergence between the two groups associated with the duration of treatment. The incidence of adverse events was 5.8% in the fidarestat group and 5% in the placebo group and no serious adverse events were noted.