An enzyme immunoassay for the quantitative measurement of CA 19-9 in serum or plasma. The sialyl Lewisa epitope is also known as the cancer associated antigen CA 19-9. CA 19-9 levels are frequently elevated in the serum of patients with cancers of the pancreato-biliary system (i.e. pancreas, gallbladder, biliary tract). In addition, elevated levels of CA 19-9 have been observed in other malignancies such as lung cancer, other gastrointestinal cancers and in some nonmalignant disorders. It must be taken into acount that patients, genotypically negative for the Lewis blood group antigen, will be unable to produce the CA 19-9 antigen even in the presence of malignant tissue.The DRG TM-CA 19-9 ELISA Kit is a solid phase enzyme-linked immunosorbent assay (ELISA) based on the sandwich principle. The microtiter wells are coated with a monoclonal [mouse] antibody directed towards a unique antigenic site of the CA 19-9 molecule. An aliquot of patient sample containing endogenous CA 19-9 is incubated in the coated well with assay buffer. After a washing step a second incubation follows with enzyme conjugate, which is an anti-CA 19-9 antibody conjugated with horseradish peroxidase. After incubation the unbound conjugate is washed off. The amount of bound peroxidase is proportional to the concentration of CA 19-9 in the sample. Having added the substrate solution, the intensity of colour developed is proportional to the concentration of CA 19-9 in the patient sample.