Introduction: Impairment of glucose tolerance increases with age in cystic fibrosis (CF) and may be associated with clinical deterioration and higher mortality. Oral glucose tolerance test (OGTT) is still considered the best test to detect glucose tolerance abnormalities, but the right time to treat glucose intolerance or diabetes is still debated. Early treatment, before clinical deterioration occurs, might be beneficial to delay complications. In this pilot study, we ought to assess whether continuous interstitial glucose monitoring, in non-diabetic CF patients, could bring additional information on their glucose tolerance. Methods: 5 CF adult patients who were not takinginsulin (3 Fy2 M, 22-34-year-old, VEMS 32-89% predicted values, BMI 18.4-24.8 kgym2), were compared to 5 non-healthy volunteers matched for sex, age, weight and height. A needle-type glucose sensor (Glucosensor^a, Medtronic) was implanted in the abdominal wall subcutaneous tissue of the subjects and connected to an electronic system that determined interstitial glucose levels every 10 sec.. At 24 h, an OGTT was performed and blood glucose level determined every 30 min. At 48 h, the system was removed. Duringthe 48 h of the study, capillary glucose levels were measured 3-4 times daily by the subjects and recorded. Results: 2 CF patients had impaired glucose tolerance according to OGTT. In one of these patients and in 2 with normal OGTT, interstitial glucose profiles showed important daily fluctuations mainly related to meals. In the other patient with glucose intolerance, glucose profile looked normal due to defective glucose detection. Discrepancy between capillary or blood levels, and interstitial glucose levels were noted in some subjects and will be discussed. Conclusions: Continuous interstitial glucose monitoring in addition to OGTT may help to assess insulin response in non-diabetic CF patients and suggests that, even when OGTT is normal, the insulin response may be abnormal.