The present invention is in the field of medicine. It relates to a method and kit for determining whether an infection is of bacterial or non-bacterial origin. It relates to a method for determining in a patient whether an infection is of bacterial or non-bacterial origin, the method comprising : (a) determining the concentration of antitrypsin (ATT) and/or of at least one fragment thereof, in a sample that has been taken from said patient, and (b) determining whether said patient suffers from an infection of bacterial or non-bacterial origin based on the concentration of ATT and/or of at least one fragment thereof and designating the infection as of bacterial or non-bacterial origin.