To recruit 150 adult patients with cystic fibrosis related diabetes (CFRD) without fasting hyperglycemia for a multi-center, twelve month, placebo-controlled intervention trial testing the ability of insulin or repaglinide to improve body mass index (BMI) and stabilize pulmonary function in cystic fibrosis (CF).

The primary objective of this research is to determine whether treatment with either insulin or an oral diabetes agent that increases endogenous insulin secretion will improve BMI and pulmonary function in cystic fibrosis patients who have diabetes without fasting hyperglycemia.

• Diabetic glucose pattern by oral glucose tolerance test (OGTT) of >200 at 120 min. (stable and healthy at time of OGTT)
• Fasting glucose levels <126.
• Weight stable within 5% in previous 3 months.
• Free from illness for two months.
• Male and female 16 and older, who are done growing
• Willing to come in for visits every 3 months.
• Patients receiving infrequent short bursts of systemic glucocorticoids may be considered for the study inclusion if: a. they have not received systemic glucocorticoids steroids for at least one month, b. they did not receive the steroids for more than 14 consecutive days or 28 days total in six months