Method for early differential diagnosis and detection, for prognosis and assessment of the severity and for therapy-accompanying assessment of the course of sepsis and sepsis-like systemic infections, in which, preferably with additional determination of at least one further parameter suitable for sepsis diagnosis, the amount of soluble cytokeratin fragments, in particular of CYFRA 21-1, TPS, TPA and/or sCY1F, in a biological fluid of a patient in whom a sepsis is present or a sepsis is suspected is determined and conclusions with regard to the presence, the expected course, the severity and/or the success of initiated measures for the therapy of the sepsis are drawn from the determined amount of soluble cytokeratin fragments.