In this research work concentrations of airborne size specific (?1, 1-1.8, <1.8 µm) microbial contaminants (endotoxin, ?-glucan) were determined using cyclone samplers in two distinctly different environments: farms and homes. Using inhalable samplers and vacuum cleaners airborne inhalable and dust contaminants from these homes were collected. This approach was used to compare PM1 microbial contaminants in a particular home with those in inhalable particles and in dust inside the same home. Samples were analyzed with Limulus Amebocyte Lysate assays for endotoxin and ?-glucan. Airway inflammation was assessed in school-age children by measuring exhaled nitric oxide (eNO) levels with non-invasive nitric oxide monitoring system (NIOX-Flex). Results indicate that PM1 endotoxin concentration may be a better predictor of airway inflammation than inhalable or larger particles Exposures to high PM1 endotoxin may protect against airway inflammation in non-asthmatic school-age children. Whether this protection is sustained, needs to be confirmed through follow-up studies.