Exhaled breath collection is used to identify and monitor inflammatory or oxidative components in breath. Exhaled breath sample collection is noninvasive and would greatly benefit human pollutant exposure research. We demonstrate the efficacy of exhaled breath collection and analysis in two human exposure studies to ozone (O(3)) and diesel exhaust, respectively. O(3) study: we collected exhaled breath (gas phase) from healthy human volunteers (age 18-35 years, 12 subjects) immediately before and after exposure to filtered air or 0.4 ppm O(3) for 2 h with and without intermittent exercise. Six subjects received antioxidant supplementation for 2 weeks before their O(3) exposure, while the remaining six subjects received placebo treatments. We demonstrate increased amounts of non-polar carbonyls exhaled immediately post O(3) exposure. The O(3)-induced increase in exhaled carbonyl concentrations was attenuated in the group receiving antioxidants. Our data demonstrate that exhaled exposure biomarkers can be measured in the breath gas phase in humans exposed to O(3). Diesel study: we collected exhaled breath condensate (EBC; liquid phase) from healthy human volunteers (age 18-40 years; 10 subjects) immediately before, immediately after and 20 h post filtered air or diesel exhaust (106 ± 9 µg m(-3)) exposure. Clean air and diesel exposures were separated by 3 weeks to 6 months. We obtained reproducible intra-subject EBC volumes and total protein concentrations across our six collection time points. Diesel exposure did not affect either EBC volume or total protein concentrations. Our data demonstrated EBC volume and total protein reproducibility over several months. Volume and total protein concentration may serve as normalizing factors for other EBC constituents.