Sanguis draxonis (SD) is a Chinese traditional herb that is prescribed for the handling of diabetic disorders. In this study, the effects of an oral administration of SD at dosages of 100, 300, and 500 mg kg 1 once a day, respectively, on the formation of insulin resistance were investigated in vivo in two models of insulin-resistant rats, HFD rats (high-fat diet-induced insulinresistant rats) and IILI rats (induced by the intraperitoneal injections of long-acting insulin at dosage of 0.5 U kg 1 three times daily). The insulin resistance was indicated using the loss of tolbutamide-induced hypoglycemic activity. After the oral administration of SD (300 and 500 mg kg 1 once a day for 7 days) to HFD rats, both plasma glucose and insulin concentration were decreased significantly, while the hypoglycemic activity of tolbutamide (10 mg kg 1, i.p.) was significantly enhanced as compared with that of the vehicle-treatment (0.9% saline solution used as vehicle to disperse SD, w/v). Moreover, the formation of insulin resistance in IILI rats had been improved significantly with SD treatment (100, 300, 500 mg kg 1 once a day for 14 days), but the influence of SD treatment on both plasma glucose and insulin concentration was not observed. For STZ-induced diabetic rats, the action of SD (300 and 500 mg kg 1 once a day for 14 days) showed more effective on an increase of response to the exogenous short-acting porcine insulin than that of the metformin administrated orally at dosage of 320 mg kg 1 three times daily. The present studies suggest that an oral administration of SD can increase insulin sensitivity and improve the development of insulin resistance in rats. # 2004 Elsevier Ireland Ltd. All rights reserved.