Equilibrium and kinetic constants were determined for interactions between alpha-amylase from Bacillus subtilis and polyclonal antibodies (with immobilization of either reagent). The effects of desorption of immobilized molecules and intermolecular complexes on the immunochemical reaction were studied. Models of sandwich enzyme immunoassay, whereby complexes of immobilized antibody-determined antigen-labeled antibody were formed, were developed from these results. The results obtained from the model and experiments were compared. The desorption was shown to cause the hook-effect, that is, a decrease in the label binding at high concentrations of the antigen.