Three main projects are included in this dissertation. Though seemingly broad in scope, this research afforded a unique opportunity for comprehensive study of urban and rural environmental inhalation exposures to endotoxin (lipopolysaccharide LPS) and the associated immune response. In the LA PM10 Endotoxin Study, ambient concentration of LPS in PM (particulate matter) was quantified through analysis of air samples collected in Southern California. Endotoxin concentrations measured were lower than recognized thresholds for adverse health effects in occupational exposures, but in the same range as for indoor effects. This study provides the first extensive characterization of endotoxin concentration across a large metropolitan area in relation to PM10 and other pollutant monitoring, and supports the need for studies of the role of endotoxin in childhood asthma in urban settings. The Mouse Whole Blood Assay (WBA) Study replicated LPS-induced airway inflammation in a laboratory model. Presently, there is a need for less invasive options for evaluating pulmonary responses to occupational exposures. The whole blood assay (WBA), which measures cytokine production of leukocytes after ex vivo stimulation with LPS, may be one such option. This study used an endotoxin-tolerance model to demonstrate the efficacy of the WBA as a biomarker of inhalation exposure to swine concentrated animal feeding operation (CAFO) dust and showed the utility of the WBA for assessing susceptibility to organic dust-induced lung inflammation. Finally, The Human WBA Study applied the WBA outside the controlled environment of the laboratory. This study utilized pulmonary function testing (PFT), symptom questionnaires and the WBA to evaluate inflammatory responses following an inhalation exposure to purified LPS in CAFO workers and controls. Subjects were stratified into response groups for analysis of WBA results based on PFT response. All subjects demonstrated significant WBA LPS-stimulant dose-responses for all 3 cytokines measured. This study demonstrated that LPS-induced pulmonary and WBA responses are variable among individuals and offered insight into the use of the WBA in future studies. Information gained from these studies provides much insight into urban endotoxin concentrations, the use of the WBA as a biomarker of pulmonary exposure in the rural environment, and offers possibilities for further research.