The invention refers to a method for in vitro diagnosis of a severe infection comprising determining delta-like ligand 1 protein or a nucleotide sequence coding for delta-like ligand 1 protein in a biological sample wherein an elevated level of expression of delta-like ligand 1 protein or a nucleotide sequence coding for delta-like ligand 1 protein is indicative of a severe infection; and the use of delta-like ligand 1 protein as a biomarker for in vitro diagnosis of a severe infection such as sepsis.