Description of the project: The main objective of this prospective biological single center study (non interventional) is to identify non invasive biomarkers able to diagnose acute GVHD and/or predict outcome of patients with acute GVHD. The primary objective of the study is double: (1): to evaluate markers as diagnostic markers of GVHD (2): to evaluate the potential of the markers as risk factor for steroid-refractory acute GVHD occurrence. Secondary objectives are: -to evaluate the markers as risk factors for GVHD -to evaluate the potential of these markers as prognostic factors of 6-month non-relapse mortality in patients with acute GVHD-to evaluate the additional value of the biomarkers to predict GVHD or steroid-refractory GVHD as compared to other known and routinely used risk factors (clinical grading system, performance status, albuminemia...). Stools and blood will be on day 7, 14, 21, 28 after transplantation and the first day of digestive GVHD. Management of patients will not differ from the usual care. Fecal calprotectin and alpha 1 anti-trypsin, plasmatic RER3a, IL-8, Elafin, TNFaR1, IL-2R alpha, HGF will be measured at each points by ELISA tests. 315 patients would be sufficient to estimate the area under the ROC curve with a half-width of the 99% confidence interval of 0.05, assuming 60% of patients would develop acute GVHD, and normally distributed markers. The diagnosis and prognosis values will be analyzed separately.