Twenty subjects will participate in two experimental periods. Each will include a 24-96 hour outpatient run-in period prior to their exercise visit wearing the bi-hormonal bionic pancreas. This will allow the bionic pancreas to adapt to their diabetes management needs. After the run-in period is complete, the subjects will participate in an exercise visit during which they will arrive fasting and remain fasted until the visit is completed. Subjects will walk on a treadmill for up to 1 hour at a comfortable walking pace. Plasma glucose (PG) measurements will be performed frequently. In one experimental period the bionic pancreas will remain in the bihormonal configuration and will deliver glucagon as needed during the exercise visit. In the other experimental period the glucagon will be replaced with a placebo during the exercise visit. The two experimental periods will be performed in random order. The study will be performed in single-blind fashion in that the participant will not know whether the bionic pancreas glucagon pump is filled with glucagon or placebo during the exercise visits. The outpatient run-in period will always be with the bi-hormonal bionic pancreas delivering glucagon.