Inclusion Criteria: 

• Individual is 2 - 80 years of age at time of enrollment.
• A clinical diagnosis of type 1 or 2 diabetes for a minimum of 6 months duration as determined via medical record or source documentation by an individual qualified to make a medical diagnosis.
• Adequate venous access as assessed by investigator or appropriate staff.
• Subjects participating in the high and low glucose challenges must have an insulin carbohydrate ratio(s) and insulin sensitivity ratio. Subjects without ratios may participate under observation only.

Exclusion Criteria: 

• Subject will not tolerate tape adhesive in the area of Guardian™ Sensor (3) placement as assessed by a qualified individual. 
• Subject has any unresolved adverse skin condition in the area of sensor or device placement (e.g., psoriasis, rash, Staphylococcus infection).
• Subject is actively participating in an investigational study (drug or device) wherein they have received treatment from an investigational study (drug or device) in the last 2 weeks.
• Subject is female and has a positive pregnancy screening test.
• Female of child bearing age and who is sexually active should be excluded if she is not using a form of contraception deemed reliable by investigator.
• Subject is female and plans to become pregnant during the course of the study.
• Subject has had a hypoglycemic seizure within the past 6 months prior to enrollment.
• Subject has had hypoglycemia resulting in loss of consciousness within the past 6 months prior to enrollment.
• Subject has had an episode of diabetic ketoacidosis (DKA) within the past 6 months prior to enrollment. 
• Subject has a history of a seizure disorder.
• Subject has central nervous system or cardiac disorder resulting in syncope.
• Subject has a history of myocardial infarction, unstable angina, coronary artery bypass surgery, coronary artery stenting, transient ischemic attack (TIA), cerebrovascular accident (CVA), angina, congestive heart failure, ventricular rhythm disturbances or thromboembolic disease.
• Subject has a hematocrit (Hct) lower than the normal reference range (please note that patients may use prior blood draw from routine care as long as done within 6 months of screening and report of lab placed with subject source documents).
• Subject has a history of adrenal insufficiency.
• Subject is a member of the research staff involved with the study.