The myo-inositol (MI) content of various nerve tissues obtained from streptozotocin (STZ)-diabetic rats was measured in order to clarify the role of abnormal MI metabolism in the development of diabetic neuropathy. Diabetes was induced in Sprague-Dawley rats by intravenously injecting 50mg/kg STZ. One group of diabetic rats was used for the experiment 3 days after the STZ injection and other group 14 days later. Weight-matched rats were used as controls. Cerebral gray matter, dorsal root ganglia (DRG), and sciatic nerve were quickly removed from those rats after decapitaton. Further, nerve cell-rich parts (DRG cells) were excised from the DRG under microscope. These samples were homogenized in 1ml of distilled water and deproteinized by adding ZnSO4 and Ba (OH) 2. Free MI in the extracts was measured by highperformance thin-layer chromatography. The MI content in the cerebral gray matter was the same in the three groups, but it was significantly decreased in the DRG cells of the 14-day diabetics. In the sciatic nerve the MI was significantly decreased in both the 3-day and 14-day diabetic rats compared with the controls. In the control group, the MI content was significantly different among the cerebral gray matter, DRG cells, and the sciatic nerve. These results indicate that the abnormal MI metabolism appears first in the distal portion of the peripheral nervous system in diabetic rats. This differnce in MI metabolism between central and peripheral nerve tissues may explain the predominant occurrence of peripheral neuropathy in diabetes mellitus.