Six five- to eight-year-old multiparous cows were given oral inoculations of sporocysts of Sarcocystis fusiformis five to six and one-half months after field breeding. All cows became ill. Clinical signs of infection included muscle tremors, hypersalivation, reduced consumption of feed, weight loss, excessive shedding of hair, elevated temperature, reduced packed cell volumes and total red blood cell counts, and abortion. One cow aborted on day 41 after inoculation, and another aborted on day 69. A moribund cow was sacrificed, and a normal fetus was found in utero. Two cows did not produce calves; in one of these cows, a fetal skeleton was found in utero at postmortem examination. One cow produced a normal healthy calf. No evidence of congenital transmission of S. fusiformis was found in histologic specimens from the fetuses or the calf. No illness or abortion was observed in any of the 25 uninoculated control cows. This paper is the first report of bovine abortion associated with experimentally induced sarcocystosis.