The National Animal Health Monitoring System (NAHMS) is sponsored by the USDA:APHIS:Veterinary Services (VS). The NAHMS Layers '99 Study was designed to provide information about the nation's layer population for education and research purposes. The USDA's National Agricultural Statistics Service (NASS) collaborated with VS to select a statistically-valid sample from 15 states for Layers '99. The 15-state target population accounted for over three-quarters of the table egg layers in the U.S. as of December 1, 1998. The study was limited to companies with 30,000 or more layer. About two-thirds (68.1 percent ) of farm sites did not allow visitors that did not have a business reason for visiting the operation in the layer houses. The percentage of farm sites that allowed non-business visitors in the layer houses did not differ by size of farm site. However, visitors were more likely to be required to sign in on farm sites of 100,000 or more layers than on farm sites with fewer layers. About two-thirds (62.9 percent) of farm sites that allowed non-business visitors required the visitors, vehicles not to have been on any other poultry farm that day. A total of 22.9 percent of farm sites did not allow business visitors, such as a salesperson or feed service personnel, in the layer houses. The average usual down time between flocks ranged from 10.5 days for farm sites in the Central region to 20.4 days in the Great Lakes region. About one-third (35.1 percent) of farm sites usually had a down time of 18 days or longer, while 8.6 percent of farm sites usually had down time of less than 4 days. The median down time was 14 days. Over 98 percent of farm sites emptied feeders and 91.3 percent emptied feed hoppers between flocks. About 80 percent each flushed water lines and dry cleaned cages, walls, and ceilings, while 71.8 percent cleaned fans and ventilation systems between each flock. Overall, less than 2 percent of farm sites had broilers, other poultry, or other domestic birds on the farm site. Contact for this paper: Lindsey Garber.