A solid-phase immunoenzymatic technique was modified to permit the detection and enumeration of antibody-secreting cells recognizing the amino or carboxy terminal of the insulin B chain. The procedure involves coating well surfaces with avidin and binding insulins specifically labelled with biotin at the B1 or B30 residue. On day 15 after immunization with human insulin, 20 outbred NMRI mice had generated cells secreting anti-insulin antibodies. The recognition of B1- or B30-related epitopes differed between individuals, suggesting that there was genetic determination of the epitopes expressed early in the immune response. The method can be used to find strains of mice with a preferential immune response to defined areas on the surface of small peptide molecules. Such strains could then be used to produce specific monoclonal antibodies.