For determining the presence and amount of human interleukin 3 (IL-3) in a sample, the present invention provides a diagnostic method, wherein an anti-IL-3-antibody, fragment or construct thereof is added to said sample under conditions which allow for binding said antibody, fragment or construct thereof to IL-3 and detecting the amount of antibody bound IL-3 in said sample, wherein the anti-IL-3-antibody is clone 13. Further subject matter of the present invention are the novel antibody clone 13, a nucleic acid encoding said antibody and a hybridoma cell line which produces antibody clone 13. A diagnostic assay kit contains all necessary reagents and materials for performing such assay, preferably an ELISA assay and especially preferably contains antibody clones 13 and 11.