We studied the effect of barley on blood glucose response in normal and diabetic rats. In the first experiment, when male Sprague-Dawley rats were fed diets containing corn starch, barley, brown rice and wheat bran for 64 days, they were administered streptozotocin (4mg/100g body weight) intraperitoneally and the corresponding diet was continued for 46 days. Glucose tolerance was suppressed in normal and diabetic rats fed the barley diet. The effect of barley was especially marked in the diabetic rats. Fasting blood glucose in diabetic rats fed barley was improved to the normal level after 25 days. Such improvements in insulin secretion and in the metabolism of glucose might play an important role in the beneficial effect of barley on the blood glucose response. A second experiment was performed to ascertain the effect of barley on diabetic rats. Glucose tolerance in diabetic rats fed barley was improved as early as 9 days, and was lower than that of normal rats fed corn starch after 33 days. These results suggest that barley could be a useful therapeutic diet for diabetic patients.