The antidiabetic potential of the alcohol root extract of Holostemma annulare Schum. (Asclepiadaceae), a medicinal plant widely used in more than 34 Ayurvedic preparations, was evaluated in the streptozotocin-nicotinamide-induced type 2 diabetic model. Graded doses of the alcohol root extract were administered to normal and experimental diabetic rats for 15 days. A significant (p <0.05) reduction was observed in the fasting blood glucose levels of normal as well as diabetic rats. Serum insulin levels were stimulated in the diabetic animals treated with the extract. Body weight, serum lipid profiles, serum urea and creatinine levels were estimated in extract-treated normal and diabetic rats. In addition, glycosylated hemoglobin and liver glycogen levels assessed in the extract-treated diabetic rats were compared with diabetic control and normal animals. Significant results were observed in the estimated parameters, thereby justifying the use of the plant in the treatment of diabetes mellitus. © 2007 Informa Healthcare.