Urinary measure of 5-hydroxyindolacetic acid (5HIAA) is an important marker for the diagnosis and follow-up of patients with small-intestine neuroendocrine tumors. Although this marker has good specificity, its sensitivity is moderate and its dosage is constraining, since it requires urine collection over 2-3 days and specific diet. Preliminary data suggested that overnight 5HIAA value may be representative of 24-hour 5HIAA value, and that plasma 5HIAA dosage could be a valuable alternative to urine 5HIAA dosage. The main objective of this study is to compare sensitivity and specificity of overnight 5HIAA value, 24-hour 5HIAA value and plasma 5HIAA value, in patients with small-intestine neuroendocrine tumors.