The effect of biotin administration on the glucose tolerance of streptozotocin (STZ)-induced diabetic Wistar rats was investigated. STZ-induced diabetes was induced by intraperitoneal injection of strepto-zotocin (45 mg/kg body weight as a single dose). The impaired glucose tolerance in response to an oral glucose load (1.8 g per kg body weight) in STZ-induced diabetic rats (STZ-rat) was partially improved by intra-peritoneal administration of biotin for 15 days (100, ag/rat/day). Howev-er, a recovery in the STZ-rat's insulin secretion was not found after biotin administration. To help clarify the mechanism underlying the improve-ment in glucose tolerance seen with biotin treatment, glucokinase and hexokinase activities were determined in the liver and pancreas. In STZ-rats that had received biotin (STZ-biotin rats), glucokinase activity was higher by 3.4-fold in liver and by 2.4-fold in pancreas than in the STZ-rats. The biotin level of STZ-rats was significantly lower in the liver and pancreas than that of the control rats (no STZ administration); but in STZ-biotin rats, the level in these organs recovered to the control level. These results demonstrate that injected biotin can improve glucose handl-ing without increasing insulin secretion in STZ-rats.