Context: No recommendations exist to inform the carbohydrate amount required to prevent hypoglycemia associated with exercise of different intensities in individuals with type 1 diabetes (T1D). Objective: The relationship between exercise intensityandcarbohydrate requirements to maintain stable euglycemia in individuals with T1D remains to be determined. It was predicted that an "inverted-U" relationship exists between exercise intensity and the amount of glucose required to prevent hypoglycemia during exercise at basal insulinemia. Our objective was to investigate this relationship and elucidate the underlying glucoregulatory mechanisms. Design, Participants, and Intervention: We subjected nine individuals (mean = SD age, 21.5 = 4.0 years; duration of disease, 11.4=6.4 years; glycated hemoglobin, 7.9=0.8% [60 mmol/mol]; body mass index, 25.4 = 5.5 kg/m2; V[overdot]O2peak, 34.8 = 5.1 mL=kg-1=min-1; and lactate threshold, 59.9 = 5.9% V[overdot]O2peak) with T1D to a euglycemic clamp, whereby euglycemia was maintained by infusing basal insulin rates with concomitant infusion of [6,6-2H2]glucose for determining glucose kinetics. Glucose was infused to maintain euglycemia during and for 2 hours after exercise of different intensities (35, 50, 65, and 80% V[overdot]O2peak). Main Outcome Measures: The glucose infusion rate (GIR), levels of glucoregulatory hormones, and rates of endogenous glucose appearance and disappearance were compared between conditions. Results: The mean GIR to maintain euglycemia during exercise increased with intensity up to 50% (4.0 = 1.6 g/h; P-.05) and 65% (4.1 = 1.7 g/h), but no glucose was required at 80% V[overdot]O2peak. Glucose rate of appearance and disappearance increased with intensity and, together with plasma catecholamines, reached higher levels at 80% V[overdot]O2peak. Conclusion: Our findings support the predicted inverted-U relationship between exercise intensity and glucose requirement. However, the relationship between iv and oral glucose requirements needs to be investigated to translate these GIR data to clinical practice. © 2016 by the Endocrine Society.