The hyperglycaemic effect of 20 g sucrose taken at the end of a regular mixed meal by diabetic patients was measured in six adult type 1 diabetics, C-peptide negative, controlled by the artificial pancreas, and twelve adult type 2 diabetics, with fasting plasma glucose levels below 7.2 mmol/l (130 mg/100 ml) and post-prandial plasma glucose levels below 10.0 mmol/l (180 mg/100 ml), treated by diet alone or with glibenclamide and/or metformin. All the patients were given on consecutive days, in random order, two mixed meals of grilled meat, green beans, and cheese, as well as a cake made either of rice, skimmed milk, and saccharine (meal A) or rice, skimmed milk, and 20 g sucrose (meal B). The meals contained equal amounts of calories and of carbohydrate. There was no difference between the meals in plasma glucose curves and plasma insulin or insulin infusion rate variations whether in peak values, peaking times, or areas under the curves, in either group of patients. Sparing use of sucrose taken during mixed meals might help well-controlled diabetic patients to comply with their daily dietary prescription while maintaining good blood glucose control.