The role of fat on carbohydrate absorption was investigated in 14 type-I-diabetics who were connected to a glucose-monitored insulin infusion pump (Biostator, Miles). The patients received test meals in the form of potatoes, rice and apples with equal carbohydrate content, in each case with and without added fat. Comparison of carbohydrate carriers showed an increase of blood sugar and insulin consumption which was biggest after the potato meal and significantly lower after rice and apple ingestion. This is probably related to the different biologic availability of carbohydrate carriers. Addition of fat caused lowering of blood sugar and insulin consumption in the potato meal; in this case nutritional fat is likely to have slowed gastrointestinal passage. There were no major differences among rice and apple. It can be concluded that addition of fat delays absorption of rapidly split carbohydrates more than absorption of slowly split carbohydrates such as rice. The lack of influence of fat on postprandial blood sugar and insulin consumption after an apple meal is related to the slight increase of blood sugar caused by the high content of fructose.