A study was conducted at a large textile mill in North Carolina to address the question: is the acute pulmonary function response of workers exposed to cotton dust for 12 hours, at a dust level greater than 2/3 the PEL (133 mg/m³) significantly different than that of workers exposed to cotton dust for 8 hours at or below the PEL (200 mg/m³). Pulmonary function tests were done on 156 workers at the following times: 1) after a break of 36 hours from work and prior to beginning a 12 hour work shift (time = 0); 2) at 8 hours into the workshift; 3) at 12 hours into the workshift; and 4) at 24 hours, prior to beginning the next 12 hour workshift. Overall, there were small but statistically significant declines from baseline (time=0) in both FEV₁ and FVC at 8, 12, and 24 hours. The mean percent changes in FEV₁ were -2.83% for 0-8 hours, -3.02% for 0-12 hours, and -1.19% for 0-24 hours. For FVC the changes were -3.11, -2.93, and -1.02 for 8, 12, and 24 hours respectively. The mean percent change in FEV₁ between 8 and 12 hours was -0.06% and for FVC +0.29%.