While the gastro-intestinal nematodes of sheep have long been a subject of inquiry in many parts of the world, similar attention has not been given to the problem in the bovine host. This may be due in part to the rarity of troublesome nematode outbreaks in cattle, as well as to the apparently greater difficulty of studying their subclinical infections. The parasitic species in cattle, sheep and goats are largely identical, but whether they represent host specific strains or are freely cross-infective has likewise been a subject of but little inquiry. Following the establishment of a new pasture designed primarily for a laboratory herd of cattle, observations have accumulated which permit orientation on certain aspects of the bovine problem. When the herd was begun, some care was taken to prevent extensive verminoses in the calves initiating it, but this attempt was not rigorous and a generous number of species later revealed their presence. While these helminthic infections have been only a subsidiary interest in the cattle, a fairly clear picture of the grade of infections which develop under such conditions has resulted. A group of sheep pastured with the cattle for two grazing seasons became infected with eight species of seven genera of the nematodes brought to the pasture by the cattle. This report also analyzes the status of flotation examinations of cattle dung and besides indicating the worm species involved in the natural experiment, gives additions from other bovine autopsies at this laboratory in comparison with three American check-lists.