Syzigium cumini, commonly known as 'jamun', is widely used in different parts of India for the treatment of diabetes mellitus. The present study was designed to evaluate the antidiabetic and antihyperlipidaemic effect of an alcoholic extract of Syzigium cumini seeds (JSEt) in alloxan diabetic rats. Diabetes was induced by single intraperitoneal injection of alloxan (150 mg kg(-1) body weight). Oral administration of alcoholic JSEt to diabetic rats at a dose of 100 mg kg(-1) body weight resulted in a significant reduction in blood glucose and urine sugar and lipids in serum and tissues in alloxan diabetic rats. The extract also increases total haemoglobin. The extract brought back all the parameters to normal levels. The effect of alcoholic JSEt was similar to that of insulin. Thus, our investigation clearly shows that alcoholic JSEt has both antidiabetic and antihyperlipidaemic effects.