The claim by some tribal populations in parts of Northern India that the young leaves of the custard apple tree, Annona squamosa L. (Annonaceae) has antidiabetic properties was investigated. Diabetes mellitus was induced with streptozotocin-nicotinamide and graded doses of the aqueous leaf extracts were then administered in drinking water to normal and experimental diabetic rats for 12 days. Fasting plasma glucose levels, serum insulin levels, serum lipid profiles and changes in body weight were evaluated in normal rats while liver glycogen levels and pancreatic TBARS levels were evaluated additionally in diabetic rats. The diabetic groups treated with the aqueous leaf extract were compared with standard glibenclamide. The findings of the study support the antidiabetic claims of Annona squamosa. © 2004 Elsevier Ireland Ltd. All rights reserved.