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Samples of the Auburn University populations of bighead carp (Aristichthys nobilis), silver carp (Hypothalmichthys molitrix) and their reciprocal hybrids were surveyed for isozyme varibility at 23 loci. Allelic variation in loci encoding for alcohol dehydrogenase, creatine kinase, lactate dehydrogenase, malate dehydrogenase (NAD-dependent) and superoxide dismutase was found to differentiate the two species. Reciprocal hybrids could not be distinguished electrophoretically. Isozyme banding patterns indicate these hybrids were diploid. These hybrids were fertile, and they produced large numbers of F2 progeny. The bighead carp population had 4% of its loci polymorphic, whereas the silver carp were polymorphic at 17% of their loci. The bighead carp evaluated in this study as well as those in previously reported studies of cultured carp, have a degree of homozygosity that is probably related to the hatchery procedures for propagating these species.