The study group will include patients with proven neuroendocrine tumors of various stages and functioning syndrome profile. A control group will be constituted with subjects having irritable bowel syndrome, in which a neuroendocrine tumor is ruled out. After providing informed consent, patients fitting with inclusion criteria will be included in the study. Patients will have to follow a specific diet, and interrupt/avoid certain medication, during the 2 days before and the 2 days during the sampling period. Whole urine samples will be collected during 2 consecutive days, in 4 parts (day1, night 1, day 2, night 2). Blood samples will be collected at the morning of days 2 and 3. Observance with diet and drug restriction will be evaluated at the morning of day 3.