This study examined the levels of ciliary neuronotrophic factor (CNTF)-like activity in the sciatic nerve of rats with short-term streptozotocin-induced diabetes or dietary supplementation with 40% galactose. CNTF-like activity, found in nerve extracts by in vitro bioassay, was reduced to 20% of control values after 1 or 2 months of galactose feeding (both P less than 0.01) and to 70% of control values after two months of streptozotocin diabetes (P less than 0.01). These data demonstrate that short-term hyperglycemia or its consequences can reduce extractable levels of Schwann cell-derived neuronotrophic factor and raise the possibility that impaired Schwann cell production of CNTF may contribute to the development of experimental diabetic neuropathy.