In this assay the Retinol Binding Protein (RBP) present in samples reacts with theanti- Retinol Binding Protein (RBP) antibodies which have been adsorbed to the surface of polystyrene microtitre wells. After the removal of unbound proteins by washing, anti-RBP antibodies conjugated with horseradish peroxidase (HRP), are added. Theseenzyme-labeled antibodies form complexes with the previously bound RBP