The Corticosterone EIA kit is a competitive enzymeimmunoassay utilising a polyclonal corticosterone antibody coated onto the inner surface of polystyrene microtitre wells. Calibrators, Controls and diluted samples are incubated with enzyme (horseradish peroxidase) labelled corticosterone in the antibody coated wells overnight at 2 8°C. The wells are washed and colour is developed using a chromogenic substrate (TMB). The absorbance of the stopped reaction mixtures are read in a microplate plate reader, colour intensity developed being inversely proportional to the concentration of corticosterone.