Technical Abstract: Studies have demonstrated that transmission of Salmonella Enteritidis (SE) within a flock could occur via the airborne route, especially in stressed birds. To investigate whether the ionizer exerted a bactericidal effect on the organisms, a sealed plastic chamber was constructed into which an aerosol containing SE was pumped. On the walls, ceiling, and floor of the chamber were attached XLT4 plates which were exposed to the aerosol for 3 hours, in the presence or absence of the ionizer. The plates were removed from the chamber, incubated at 37C for 24 hours, and then counts were made. Greater than 1000 CFU/plate were observed on plates exposed to the aerosol without the ionizer compared with less than 20 CFU/plate on the ionizer exposed plates. Experiments where, after being exposed to the 3 hour aerosol, the inside surfaces of the chamber were rinsed with 100 ml PBS and the rinse plated onto XLT4 plates, showed that, while the rinse from the chamber exposed to the aerosol in the absence of the ionizer contained colony counts greater than 400 CFU/ml of wash, no colonies were found in the rinse from ionizer-exposed chambers. These results indicate that negative air ionization can have a significant impact on the airborne microbial load in a poultry house and at least a portion of this effect is through direct killing of the organisms.