Acute cross-shift respiratory changes were evaluated for workers at 25 farms in northeastern Colorado during the summer of 1994 wheat harvest. Information on workers' respiratory health, past occupational exposures, and smoking status was obtained. Each worker was asked to rank eight acute symptoms before he or she began harvest work for the day. Spirometry was also performed before work began. Each participant wore a high-flow personal air sampling pump for the full shift. At the end of the workshift, spirometry and ranking of the eight acute symptoms were conducted again. Total dust exposure was determined gravimetrically. Total endotoxin was measured by the Limulus amoebocyte lysate (LAL) assay. The 98 harvest workers included in the study ranged in age from 18 to 80. Ten percent of the workers had moderate airway obstruction, as indicated by the pre-shift spirometry test results. Fifty percent of the workers were current or ex-smokers. Despite an unusually poor harvest, total dust exposures ranged from 0.09 to 15.33 mg/m3 (geometric mean 0.83 mg/m3), with 8 percent of workers exposed above the American Conference of Government Industrial Hygienists (ACGIH) threshold limit value (TLV) of 4 mg/m3. Total endotoxin exposures ranged from 4.4 to 744.4 EU/m3 (geometric mean 54.2 EU/m3), with 33 percent of workers exposed above 90 EU/m3, the level suggested as a threshold for acute mucous membrane irritation and pulmonary change among cotton workers. Sixty percent of workers experienced a cross-shift change in at least one respiratory symptom. The respiratory index (sum of cross-shift changes in the eight acute respiratory symptoms) was significantly correlated with both total dust and endotoxin exposure. Cross-shift changes in the spirometric variables were associated with smoking status, age, presence of airway obstruction, and history of chronic respiratory symptoms, but not with dust or endotoxin exposure. Peak expiratory flow rate was found to decrease over the workshift in a manner similar to that experienced by cotton workers.