The incidences of allergies, allergic diseases and asthma are increasing world wide. Global climate change is likely to impact plants and animals, as well as microorganisms. The World Health Organization, U.S. Environmental Protection Agency, U.S. Department of Agriculture, U.S. Department of Health and Human Services, and the Intergovernmental Panel on Climate Change cite increased allergic reactions due to climate change as a growing concern. Monitoring of indoor and ambient particulate matter (PM) and the characterization of the content for biological aerosol concentrations has not been extensively performed. Samples from urban and rural North Carolina (NC), and Denver (CO), were collected and analyzed as the goal of this research. A study of PM(10) (<10 mu m in aerodynamic diameter) and PM(2.5) (<2.5 mu m in aerodynamic diameter) fractions of ambient bioaerosols was undertaken for a six month period to evaluate the potential for long-term concentrations. These airborne bioaerosols can induce irritational, allergic, infectious, and chemical responses in exposed individuals. Three separate sites were monitored, samples were collected and analyzed for mass and biological content (endotoxins, (1,3)-beta-D-glucan and protein). Concentrations of these bioaerosols were reported as a function of PM size fraction, mass and volume of air sampled. The results indicated that higher concentrations of biologicals were present in PM(10) than were present in PM(2.5), except when near-roadway conditions existed. This study provides the characterization of ambient bioaerosol concentrations in a variety of areas and conditions. Published by Elsevier Ltd.