To compare blood glucose (BG) responses during a 60 min moderate intensity exercise session performed in early or late postprandial periods. Nine generally well-controlled (HbA(1c): 7.3+/-0.1%) type 1 diabetic patients performed, at least one week apart, two exercise sessions, 60 (early exercise) and 180 min (late exercise) after a standardized breakfast. All subjects were using Humulin N (N) and Humalog (Lispro, LI) insulin. During exercise, the overall decrease in BG was 4.8+/-0.6 mmol/l and 3.6+/-0.8 mmol/l in early and late exercise, respectively (P=0.051). To prevent hypoglycemia, a dextrose infusion was initiated when BG reached 5 mmol/l. The quantity of dextrose infused was 6.2+/-3.0 g and 10.5+/-3.2g in early and late exercise, respectively (NS). The time free of dextrose infusion during exercise was 41.2+/-7.8 min and 31.7+/-7.5 min in early and late exercise, respectively (NS). In N-LI users, overall drop in BG during exercise tends to be greater in the early postprandial period. However, early and late exercise present similar quantity of dextrose infused and time free of dextrose infusion. Consequently, the similar risk of exercise-induced hypoglycemia suggests similar precautions in either exercise times.