Non-smoking human volunteers aged 18-35 were exposed to aerosols of 1 mg/m³ cotton dust for 5 hours in an experimental cardroom. Spirometry and nasal lavage were done prior to exposure and repeated immediately after exposure. Subjects were categorized as atopic or nonatopic based on their response to a screening questionnaire. Atopic status was confirmed by a quantitative serologic test. The group mean decline in FEV(1) was -6% for all subjects. Confirmed atopics had a significantly larger decline in FEV(1) (-8.3%) than nonatopics (-4.9) (p<0.001). Cell counts in post-exposure nasal lavage increased an average of 212% over preexposure lavage counts for all subjects (P=0.05). For non-atopics there was a significant increase in cell counts (319%) from pre-to post-exposure nasal lavage (p<0.01). For atopics there was no difference in cell counts between pre-and post-exposure lavage. These data indicate that atopics are more responsive to aerosols of cotton dust than non-atopics when using airflow measurements as a marker of reaction. A similar increase in responsiveness was not observed in atopics when using change in cell count as a marker of reaction, however cell number may be an indicator of baseline inflammation and the elevated cell counts in pre-exposure lavage of atopics may be a marker of increased airway reactivity which would result in increased responsiveness.