Diagnosing and Treating Low Blood Sugar Levels

Hypoglycemia is the term used to refer to lower than normal levels of blood sugar. This study will continue to research the causes of hypoglycemia. Patients involved in the study will be admitted to the Clinical Center of the National Institutes of Health and undergo tests for evaluating blood sugar. Patients will be required to refrain from eating for a set period of time and will undergo blood tests for insulin levels and several other specific diagnostic tests related to insulin secretion. The patients will be under supervision and will be provided with appropriate medical and surgical attention as needed.

* INCLUSION CRITERIA: In order to be eligible to participate in this study, an individual must meet all of the following criteria: 1. Male, females ages \>= 18. 2. Patients with documented fasting blood glucose below 55 mg/dl. 4\. Patients with biochemical evidence for insulinoma or other pancreatic neuroendocrine tumors. EXCLUSION CRITERIA: An individual who meets any of the following criteria will be excluded from participation in this study: 1. Patients with significant cardiac disease will be excluded. 2. Subjects who are pregnant per self-report. 3. Medically unstable per the assessment of the PI.