Although the merit of polyvalent antivenoms is well-recognized, there is still doubt in some medical circles as to the relative efficacy and the propensity to cause adverse reactions of polyvalent (pAV) as compared to monovalent (mAV) antivenoms. Immunochemical and biochemical comparisons of equine polyvalent and monovalent antivenoms prepared under the same immunization protocols were therefore made. These antivenoms were prepared against Naja kaouthia (NK), Ophiophagus hannah (OH) and Bungarus fasciatus (BF) venoms. SDS-PAGE analysis of both types of antivenoms showed similar serum protein profiles. The total amount of immunoglobulin (IgG(T)+IgG) in pAVs was slightly but significantly higher than that of mAVs, while the total serum protein content in mAVs was slightly but significantly higher than that of pAVs. The amounts of total hyperimmune IgG(T), determined by ELISA, were similar in mAVs and pAVs. pAVs contained specific antibodies against the principal NK postsynaptic toxin (NK 3) to the same extent as that observed with the anti-N. kaouthia mAV. The antibodies against OH and BF principal postsynaptic toxins (OH II and BF IX) in pAVs were significantly higher than those of the corresponding anti-O. hannah and anti-B. fasciatus mAVs. These results were in concordance with the comparable in vivo neutralization activities of mAVs and pAV previously reported. The apparent dissociation constant (Kd) of anti-OH II antibody in pAVs was comparable to that of the anti-O. hannah mAVs. The apparent K(d)s of anti-NK 3 and anti-BF IX antibodies in the corresponding mAVs were slightly lower than those in pAVs. The Kd values were all in nM range and were considered to be high affinity binding. It is concluded that pAVs could be prepared with potency and protein contents and thus the propensity to cause adverse reaction that were comparable to those of mAVs.