$M_4$-LDH isozyme was partially purified from the skeletal muscle of Agkistrodon blomhoffii brevicaudus. The protein was injected into rabbits and the resulting antiserum was tested for reactivity with crude preparations of LDH isozymes of fifteen vertebrate species. Antisera against $M_4$-LDH isozyme of A. blomhoffii brevicaudus reacted very strongly with the LDH isozymes, except the $H_4$-LDH isozyme, of A. saxatilis and A. caliginosus but weakly with those of Rhabdophis tigrinus at fixed conditions. A. caliginosus showed a difference in the immunodiffusion test and was considered to be a species less related to others of genus Agkisrodon. The suggestion that the H and M lactate dehydrogenase subunits are immunclogically distinct has been reaffirmed in the present study.