An electrophoretic survey was conducted to estimate the amount of genetic variation that was detectable in proteins of grass carp stocks being artifically propagated in the United States. Staining procedures for nonspecific protein and 18 specific enzymes revealed an estimated 49 loci among the five tissues that were examined. The three polymorphic loci identified included the enzymes phosphoglucose isomerase (PGI) and esterase (Est), and the serum protein haptoglobin (Hp). The somewhat low average heterozygosity per locus (0.021) was partially attributed to the fact that four of the five stocks examined were derived from progeny of a single mating. This small common gene pool indicates that these stocks are inbred relative to wild populations and are therefore probably less capable of adapting to suboptimal spawning conditions. The intentional breeding of different homozygous combinations of variant alleles in hatchery stocks is recommended as an effective means of monitoring the spread and the relative contributions of these stocks.