The human IL-12/-23 (p40) ELISAPRO kit provides all necessary reagents and solutions required to quantify human IL-12/-23 (p40) in solution, e.g. in cell culture supernatant, and serum/plasma samples. The kit contains ELISA plates pre-coated with monoclonal capture antibodies, biotinylated detection antibody, Streptavidin-HRP, TMB substrate, ELISA standard and ELISA diluent. The ELISA diluent prevents false positive read-outs which may be caused by heterophilic antibodies found in serum and plasma samples.