Vitamin B mixture, especially a mixture of B1, B6, and B12, provides beneficial effects when used for the clinical treatment of various types of neuropathy including that in diabetes (1). In diabetic neuropathy, a decrease in nerve conduction velocity (NCV), segmental demyelination in nerve fibers, and an impairment of Schwann cells are observed in peripheral nerves (2). In animal experiments, thickening and degeneration of the myelin sheath are observed in both alloxan and streptozotocin (STZ) diabetic rats, and this demyelination may result in the reduction of NCV observed in diabetic rats (3-5). NCV is used as a major diagnostic and therapeutic index for assessing the function of peripheral nerves in diabetic neuropathy. Iwata et al. (6) and Fukuda et al. (7) reported an ameliorating effect of vitamin B mixture (B1, B6, and B12) on the decrease in NCV in alloxan diabetic rats. However, there is little information concerning the effects of vitamin B mixture on STZ-induced diabetic neuropathy, which is considered the preferable model for studying severe diabetic peripheral neuropathy (8). Thus, we investigated the effects of daily administration of 3B (a mixture of thiamine disulfide, pyridoxal hydrochloride and aquocobalamin) on STZ-induced diabetic neuropathy using NCV as the index. In accordance with a previous report (9) which demonstrated the favorable effects of a high dose of 3B on neuropathy induced by acrylamide, we also adopted a relatively high dose of 3B.The experiments were carried out on 3 groups of male Sprague-Dawley rats (9 weeks old, n=14-19). A standard laboratory chow (CRF-1, Charles River) and tap water were always available. Daily intake of vitamin B1, B6, and B12 from the diet was approximately 1.5, 0.5, and 0.0075mg per rat, respectively. Two groups were made diabetic by intraveneous injection of 45mg/kg STZ (Sigma) dissolved in citrate buffer (pH 4.1) immediately before use. The third group received the citrate 95

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