Die-Huang-Wan is a herbal mixture widely used in Chinese traditional medicine to treat diabetic disorders. We have investigated the effect of Die-Huang-Wan on plasma glucose concentration in-vivo. Die-Huang-Wan was administered orally (5.0, 15.0 or 26.0 mg kg(-1)) to three rat models. Wistar rats were used as the normal animal model, rats with insulin-resistance (induced by the repeated thrice daily injection of human long-acting insulin) were used as the non-insulin-dependent diabetic model, and streptozotocin-induced diabetic rats were used as the insulin-dependent diabetic model. In normal rats, approximately 1 h after oral administration of Die-Huang-Wan the plasma glucose concentration decreased significantly in a dose-dependent manner, from 5 to 26.0 mg kg(-1). A similar effect was observed in rats with insulin-resistance. However, this effect was not observed in streptozotocin-induced diabetic rats, even at an oral dose of 26.0 mg kg(-1). These results suggested an insulin-dependent action, a view supported by the increase of plasma insulin-like immunoreactivity in normal rats receiving Die-Huang-Wan. The results indicated that Die-Huang-Wan had an ability to stimulate the secretion of insulin and this preparation seemed helpful in improving the diabetic condition, especially hyperglycaemia in type-II diabetes.