To evaluate the clinical utility of nasal lavage (NL), we performed post-work shift NL on 172 grain workers and 78 postal worker control subjects. The grain worker group included a higher percentage of current smokers (25.7% vs 16.7%) and a lower percentage of former smokers (21.1% vs 35.9%) compared with the postal workers. The control subjects included more female workers and were slightly older than the grain workers. Compared with the postal workers, the grain workers were exposed to significantly greater concentrations of total dust (0.1±0.0 vs 6.8±1.4 mg/m3; mean ±SEM) and total endotoxin (4.3±0.8 vs 2,372.4±653.8 endotoxin units/m3). NL from grain workers showed a higher concentration of total cells (55,000±14,000 vs 25,000±5,000 cells per milliliter; p=0.03), a higher concentration of squamous epithelial cells (17,029.0±4,177.0 vs 7,103.7±1,479.8 cells per milliliter; p=0.03), and a higher concentration of neutrophils (40,058.0±12,803.2 vs 17,891.0±3,822.3 cells per milliliter; p=0.10) compared with postal workers. Importantly, these differences in NL cellularity between grain workers and postal workers were observed within the three strata of smokers. To further assess the importance of total cells, squamous epithelial cells, and neutrophils in the NL fluid of grain workers, we investigated the relationship between these cell concentrations and (1) measures of dust and endotoxin exposure during the work shift, (2) spirometric measures of airflow obtained immediately before the NL, and (3) work-related respiratory symptoms. The concentration of total cells, the concentration of squamous epithelial cells, or the concentration of neutrophils in the NL was not associated with ambient levels of dust or endotoxin, with baseline or cross-shift changes in lung function, or with work-related respiratory symptoms. These findings suggest that increased NL cellularity may be seen in workers exposed to high dust levels. However, the NL cellularity does not appear to be associated with ambient concentrations of dusts or endotoxins, with signs of airflow obstruction, or with work-related respiratory symptoms.