Four carbohydrate diets with different glycaemic index were fed to 10 type I diabetic patients on continuous subcutaneous insulin infusion (CSII). Every diet consisted of 4 meals with identical carbohydrate content, being consumed during one day each at 8.00, 12.00, 16.00 and 18.00 h. CSII was conducted according to the patients' experiences, aiming at plasma glucose values between 70 and 160 mg/dl. From 8.00 to 20.00 h, plasma glucose was measured every 2 h. Plasma glucose profiles were near-normal with all of the diets; differences between the diets were statistically insignificant. The premeal insulin dosages, as delivered by the patients, varied significantly in relation to the time of the day, and to the premeal plasma glucose concentration. The patients varied their prandial insulin doses also in relation to the 4 diets, indicating that the glycaemic index was helpful for the prediction of their prandial insulin requirements. It is concluded that near-normoglycaemia can be achieved in type I diabetic subjects on CSII irrespective of the glycaemic index of their diet, if the prandial insulin requirements are met adequately.