The National Animal Health Monitoring System (NAHMS) is sponsored by the USDA:APHIS:Veterinary Services (VS). The NAHMS Equine '98 Study was designed to provide information about the nation's equine population for education and research purposes. Equine viral arteritis population for education and research purposes. Equine viral arteritis (EVA) is an infectious disease caused by the equine arteritis virus (EAV). It can cause abortion in pregnant mares and death in young foals. Breeding stallions may become permanent carriers of the virus. Financial losses may include those due to abortion and/or disease and death in very young foals, reduced demand to breed and/or decreased commercial value of persistently infected stallions, and denied export market for infected animals. Overall, 59.4 percent of operations had never heard of equine viral arteritis. The percentage of operations that knew some basics or were knowledgeable regarding EVA increased with size of operation, from 7.6 percent of operations with one to five horse to 27.3 percent of operations with 20 or more horses. the percentages of operations that were familiar with EVA were highest in the racing (31.9 percent) and breeding (31.3 percent) categories of horse use and the lowest in the farm/ranch category. Of horses vaccinated against EVA, 25.3 percent were seropositive; of horses not vaccinated against EVA, 2.0 percent were seropositive. However, due to the very small number of operations that vaccinated (1.6 percent), these unvaccinated horses with a titer to EAV was higher (17.4 percent) on operations which had taken a horse outside of the state within the previous 12 months than on those operations that did not take the horse out of the state (5.4 percent). The percentage of horses of the Standardbred breed with positive EAV titer was higher (23.9 percent) than percentages for Thoroughbred (4.5 percent), Quarter Horse (0.6 percent), Warmblood (3.6 percent), and other (1.3 percent) breeds. Contact for this paper: Lindsey Garber.