We have developed an immunoassay for screening large libraries of potential catalysts of a bimolecular Diels-Alder reaction. The procedure involves the reaction of immobilized dienophile with diene in solution and subsequent detection of the product with a monoclonal antibody as in a regular enzyme-linked immunosorbant assay (ELISA). The assay exhibits the expected dependence on time and diene concentration. A catalytic antibody accelerates the reaction in a concentration dependent manner despite immobilization of the dienophile, and its catalytic efficiency is comparable to that in free solution. The current study explores both the utility of this assay and criteria for its successful application to other reactions. Employment of this strategy, previously dubbed catELISA (Tawfik, et al. PNAS 1993, 90, 373), to monitor a bimolecular cycloaddition reaction supports its potential as a general approach to screening for catalysts.