Virtually all patients with type I diabetes are familiar with inexpli cable fluctuations in blood glucose concentration that expose them to both hypoglycemia and hyperglycemia. It is commonly assumed that such fluctuations are due, in large part, to varia tions in food intake, physical activities, and emotional state. However, substantial day-to-day variation in blood glucose concentration is observed when diet, exercise, emotional state, insulin dosage, and timing of insulin administration are held constant. This suggests that variation in the rate of absorption of insulin from the subcutaneous injection sites may be an important factor causing those fluctuations. Variations in insulin absorption are increased if the anatomic regions used for injec tions are rotated. A recent study completed at the University of Minnesota Hospital and Clinic indicates that it is inadvisable for type I diabetic subjects to rotate insulin injection regions; rather, insulin injections should be confined to a single anatomic region (usually the abdomen) as this will decrease day-to-day variability in blood glucose concentration. Such a decrease should allow greater precision in adjusting insulin doses, thereby helping achieve good control.