Localization of thiamine in the ligated and unligated sciatic nerve of rats was studied histochemically and biochemically. Thiamine content increased, up to 200% of the unligated nerve, in the nerve just above the ligation 48 hr after surgery. This accumulation of thiamine was observed in the axoplasm just above the ligation. Thiamine in the unligated sciatic nerve exhibited a proximodistal gradient of concentration. The data suggest that accumulation of thiamine is due to the proximodistal streaming of axoplasm.