There is little information concerning the extent of parasitic infestation in cattle, particularly subclinical infestations. Relatively few experimental studies of parasitic infestations in cattle have been made. This is due, in part at least, to the high cost of cattle as experimental animals and the space required for conducting experiments on them. Internal parasites have long been recognized as a hazard in the production of sheep and swine but comparatively few livestock raisers realize that in many instances parasites cause serious losses in cattle. Even when parasites are present in sufficient numbers to produce clinical symptoms, these symptoms are often confused with and ascribed to other conditions. This is particularly true in those areas where parasitism occurs in conjunction with malnutrition.