In addition to the bispecific antibody, the hybrid-hybridoma 28.19.8 secretes antibodies monospecific for carcinoembryonic antigen (CEA) and antibodies monospecific for vinca alkaloids. By exhaustive affinity purification, the immunoglobulins isolated by Protein A chromatography from ascitic fluid have been fractionated into four populations, three of which are immunoreactive. Studies on these fractions by FPLC, SDS-PAGE, and a variety of ELISAs have shown that seven of the ten possible combinations of heavy and light chains exist as immunoreactive forms. The results suggest that the other three inactive combinations are also secreted by the hybrid-hybridoma.