The purpose of this 2-year project was to investigate the transmission of PRRSV and Mycoplasma hyopneumoniae (M hyo) by aerosols, the meteorological conditions associated with this route of spread and biosecurity strategies to reduce this risk. At this time, year 1 of the project has been completed. Airborne spread of PRRSV and M hyo has been documented in animals housed in the non-filtered facility while no evidence of transport or transmission of either agent has been observed in the filtered facility. Collection of weather data is ongoing; however, directionality of predominant winds appears to be an important factor associated with the risk of airborne spread of both agents. Additional information generated during concurrent studies conducted in year 1 included documentation of PRRSV transport by air during nighttime in summer and proof of the ability of both agents to be transported by aerosols over distances out to 4.7 km. Year 2 of the project will focus on airborne spread of both agents but will incorporate 2 different air filtration methods (MERV 14 mechanical filters and antimicrobial filters) in order to enhance lower cost-alternatives to MERV 16 systems.