Twenty four diabetic patients (12 type 1 and 12 type 2) were studied to determine the influence of using foods rich in carbohydrates with either low or high glycemic indexes on the glycemic control of Diabetes Mellitus. All patients were treated with insulin. During 2 periods of 4 weeks the patients received, at lunch, 2 types of foods rich in carbohydrates as part of their usual diet. Meal A: foods with a low glycemic index and Meal B: foods with a high glycemic index. During the last 7 days of each period the patients determined, at home, their capillary glucose levels before and 1, 2, and 3 hours after lunch by means of a reflectometer. At the end of each period HbA1 levels were also determined. No differences in insulin dose or changes in body weight were found during the two periods of the study for both types of diabetic patients. Capillary glucose levels before lunch were similar on both diets and for both types of diabetic patients. Similarly, postprandial capillary glucose levels 1, 2, and 3 hours later were not different for both died A and diet B. No statistically significant differences were found either in HbA1 values for both periods of the study. These results confirm previous ones obtained in acute studies. The present findings indicate that the glycemic response of foods rich in carbohydrates is modified when included in a mixed meal by the other components of the meal. From these date it can be inferred that the use in a diet of foods with a low glycemic index does not improve the glycemic control of patients affected of Diabetes Mellitus.