This paper describes a new method for precise determination of viral aerosol lethal close (ALD(50)) and reports the results obtained for birds exposed by H5N1 Avian influenza A strain under controlled laboratory conditions The reported method utilizes Our recently developed personal bioaerosol sampler capable of monitoring viable virus concentration in the ambient air. Up to six laboratory animals Could be located in a specially designed aerosol chamber and exposed in parallel by an airborne strain of interest to generate the amount of data sufficient for representative statistical analysis A concentration of viable airborne virus was measured by the personal aerosol samplers directly in the breathing zone of each particular bird The results show a very low inter-sampler variation used for each particular run. which was confirmed by a single factor ANOVA test undertaken for all six personal samplers involved in each experiment As was shown, the difference in amount of viruses collected by all samplers during each particular run was not statistically significant. It was found that the ALD(50) for approximately 400-g birds exposed to H5N1 Avian influenza A strain A/Chicken/Suzdalka/Nov-11/2005 was around 26 5 FFU (focus forming units) (c) 2009 Elsevier Ltd. All rights reserved