Bioaerosols generated during livestock and poultry production are significant occupational hazards. This study investigates the characteristics of bioaerosols released from animal feces. Fresh feces from pigs and chickens were obtained and tested in a controlled-environment facility. Airborne viable (culturable) bacteria and fungi were sampled hourly for 48 hr. The predominant species were identified via polymerase chain reaction analysis. The number of bacterial colonies released from chicken feces increased gradually, peaked at approximately 20 hr, and remained relatively constant to test end; however, the bacterial colonies released from swine feces did not increase significantly. The chicken feces released significantly (P < 0.05) more bacterial aerosols than swine feces over 40 hr, by approximately 1 order of magnitude. However, the difference in total fungal aerosols released from the two feces types was relatively small (30-40%) and insignificant (P > 0.05). Aerosols sized between approximately 0.65 and 1.1 microm were predominant for bacteria, whereas aerosols sized between approximately 2.1 and 3.3 microm prevailed for fungi. Genera Stenotrophomonas were the predominant bacterial aerosols, whereas Cladosporium and Acremonium accounted for the greatest amounts of fungi from chicken and swine feces, respectively. More than 1000 culturable bacterial colonies can be released from 1 g of chicken feces per hour, and approximately 80% of these bioaerosols are respirable. Most bacterial aerosols released from swine and chicken feces were opportunistic human pathogens; thus, the significance of their presence warrants further investigations.