Dietary antioxidant compounds such as flavonoids may offer some protection against early-stage diabetes mellitus and its complications. Abnormalities in both glucose metabolism and lipid profile constitute one of the most common complications in diabetes mellitus. The present study aimed to evaluate the effect of rutin, through biochemical parameters, on experimental streptozotocin (STZ)-induced diabetes in rats. Male Wistar rats were divided into four groups: untreated controls (GI); normal rats receiving rutin (GII); untreated diabetics (GIII); diabetic rats receiving rutin (GIV). STZ was injected at a single dose of 60 mg kg(-1) to induce diabetes mellitus. The diabetes resulted in increased serum glucose, cholesterol, triacylglycerols and lipoproteins (LDL and VLDL-cholesterol) but decresed serum HDL-cholesterol and insulin. Rutin (50 mg kg(-1)) reduced (p<0.05) blood glucose and improved the lipid profile in STZ-induced diabetic rats. Alanine aminotransferase (ALT), aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) activities were significantly augmented in serum of STZ-diabetic rats, while these activities were diminished in hepatic and cardiac tissues compared with the control group. Rutin prevents changes in the activities of ALT, AST and LDH in the serum, liver and heart, indicating the protective effect of rutin against the hepatic and cardiac toxicity caused by STZ. Rutin was associated with markedly decreased hepatic and cardiac levels of tryacylglycerols and elevated glycogen. These results suggest that rutin can improve hyperglycemia and dyslipidemia while inhibiting the progression of liver and heart dysfunction in STZ-induced diabetic rats.