This study was performed to evaluate the aerodynamic size distribution and viability of the aerosolized H1N1 virus particles. Freeze-dried H1N1 was suspended in filtered sterile deionized water to a concentration of 34x105 PFU/ml (plaque forming unit per milliliter) as the virus stock suspension and incubated at 4o C. The virus solution was aerosolized at air flow rates of 2, 6, 12 L/min by using a Collison nebulizer. The aerodynamic particle sizer spectrometer was used to measure the virus aerosol particle size profile at intervals of 1, 15, 30, 45, and 60 minutes. Aerosolized samples in triplicate were trapped in a quenching medium for viable enumeration. The data indicated that the number frequency mode for approximately 35 nm size particles for the 1 min of duration, was slightly less than the individual H1N1 virus size (~50 nm). However, the virus particle size spectrum produced by the Collison nebulizer exhibited an increase in fragments, as deduced from a 20% rise in modal frequency, when operated at an air flow rate of 12 L/min and over 60 min of continuous virus aerosol generation. In addition, measurements of H1N1 virus viability revealed a 40% loss for the samples collected at 60 min intervals, which can be explained as the effects of shear and impact stresses on biological agents (H1N1) as well as carrier fluid reuse commonly encountered in a Collison nebulizer. These trends are in good agreement with previous studies for aerosolization of bacterial agents using a Collison nebulizer.