This assay employs the competitive inhibition enzyme immunoassay technique. The microtiter plate provided in this kit has been pre-coated with an antibody specific to retinoic acid. Standards or samples are added to the appropriate microtiter plate wells with Horseradish Peroxidase (HRP) conjugated retinoic acid. The competitive inhibition reaction is launched between with HRP-conjugated retinoic acid and retinoic acid in samples. A substrate solution is added to the wells and the color develops