Coccidiosis, a complex intestinal disease that is of major economic importance in domestic animals, is caused by the Eimeria species. The coccidia have enormous impact on the domestic poultry and cattle industries of the world because of the mortality, morbidity, and weight loss that the infection produces. A conservative estimate of the current losses to coccidiosis, based on 6- to 16-year-old data, is at least one billion dollars annually. 1 , 2 Control of the coccidia is primarily through the use of anticoccidial compounds; their importance is demonstrated by the direct relationship between the growth of the poultry industry and the development of the anticoccidials. 3 However, the increased costs of clearing a compound for use in food animals, which has resulted in reduced development of anticoccidials, and the resistance of the coccidia to a number of compounds already on the market, suggest that other means of control, such as subunit vaccines, may become necessary.