Rationale: Grain workers report adverse respiratory symptoms, due to exposures to grain dust and endotoxin. Studies have shown that biomarkers in exhaled breath condensate (EBC) vary with the severity of airway inflammation. Objectives: The purpose of the study was to evaluate biomarkers of airway acidity (pH and ammonium) and oxidative stress (8-isoprostane) in the EBC of grain workers. Methods: 75 workers from 5 terminal elevators participated. In addition to EBC sampling, exposure monitoring for inhalable grain dust and endotoxin was performed; spirometry, allergy testing, and a respiratory questionnaire derived from the American Thoracic Society were administered. Measurements and Main Results: Dust and endotoxin levels ranged from 0.010 to 13 mg/m³ (median: 1.0) and 8.1 to 11000 EU/m³ (median: 610) respectively. EBC pH values varied from 4.3 to 8.2 (median: 7.9); ammonium values from 22 to 2400 µM (median: 420) and 8-isoprostane values from 1.3 to 45 pg/ml (median: 11). Univariate and multivariable analyses revealed a consistent effect of chronic smoking and obesity with decreased pH and ammonium, and intensity of grain dust and endotoxin with increased 8-isoprostane. Duration of work on the test day was associated with decreased pH and ammonium, while duration of employment in the industry was associated with decreased 8-isoprostane. Conclusions: We conclude that chronic exposures are associated with airway acidity while acute exposures are more closely associated with oxidative stress. These results suggest that collection of EBC may contribute to predicting the pathological state of the airways of workers exposed to acute and chronic factors.