This study compared the filtrating efficiency (FE) of a commercial electronic air filter for filtering bacteria and viruses from contaminated air with a high efficiency particulate air (HEPA) filter. An enclosed chamber was constructed, in the middle of which an air filter was placed for testing. MTB H37Ra and T7 virus at concentrations of 5x10(8) each were sprayed into one side of the chamber using a nebulizer and the sprayed samples were collected by an impinger air-sampler on the other side. MTB and T7 viruses were detected by PCR and culture. The PCR could detect samples down to 10 fg for MTB H37Ra and 1 pg for T7 virus. Most MTB H37Ra sprayed failed to culture. S. aureus at a concentration of 10(5) cfu and E. coli at a concentration of 10(4) cfu along with T7 virus were filtered out with a FE of more than 99%. T7 virus has a particle size of 0.04 microm, S. aureus has a particle size of 1 microm and E. coli has a particle size of 2 microm.