Seven polymeric forms and conjugates of purified principal postsynaptic neurotoxins of Naja naja siamensis (NNS), Ophiophagus hannah (OH) and Bangarus fasciatus (BF) have been synthesized by controlled polymerization in which only 29-60% of the toxins were allowed to react. A carbodiimide (ECDI) and glutaraldehyde (GA) were used as coupling agents while BSA and tetanus toxoid (TT) were used as carriers. The antigenic mosaic of these immunogens was: NNS-ECDI, NNS-BF-OH-ECDI, NNS-BSA-ECDI, NNS-TT-ECDI, NNS-BF-OH-TT-ECDI, NNS-GA and NNS-BF-OH-GA. By using SDS-PAGE and radioactive toxin, each immunogen preparation was characterized in terms of molecular size and abundance of protein components, percent toxin reacted and toxin density. The relative immunogenicities of the immunogens along with those of NNS venom and pure NNS neurotoxin were evaluated in groups of eight rats. The levels of specific antibody against each of the neurotoxins were determined by ELISAs. Multiple comparisons between antibody responses to these immunogens were made. All the chemically modified immunogens were at least as immunogenic as NNS venom. NNS-TT-ECDI gave the highest antibody response (2.7-6.2-fold higher than that induced by NNS venom). All three multispecific immunogens induced comparable specific antibodies to BF, OH and NNS neurotoxins. The results showed that the presence of TT carrier and the relative degree of toxin density affected the immunogenicities. Some of the immunogens reported here should be useful for the production of potent, polyvalent antivenoms against elapid snakes.