Exposure to cotton dust can result in acute pulmonary inflammation marked by elevation of neutrophils in nasal and bronchoalveolar lavage fluids and by activation of alveolar macrophage. Such exposure may also result in chest tightness and airway constriction. For this reason, OSHA has established a permissible exposure limit (PEL) of 0.2 mg/m³ for yarn manufacturing and cotton washing. This PEL is for an 8 hr workday. Questions concerning an appropriate standard for extended workdays (longer than 8 hrs) have been raised. As an initial attempt to address this issue, we employed a guinea pig model exposed to 1.5 mg/m³ of cotton dust for 4-16 hrs and monitored pulmonary inflammation 0 and 18 hrs post-exposure. Total bronchoalveolar lavage cells, leukocytes, and red blood cells increased linearily with total exposure (concentration x exposure time) both immediately and 18 hours post-exposure. Macrophage activity, measured as zymosan-stimulated chemiluminescence, exhibited a similar linear relationship to total exposure. These animal results suggest that the concentration-time product may be an appropriate exposure metric when evaluating the risk of acute inflammation in response to cotton dust.