We studied 248 grain handlers and 192 city services workers (control subjects) before and after an 8-h work shift and measured total dust levels using personal samplers. We found that grain workers exposed to a mean total dust level of 3.3 +/- 7.0 mg/m3, when compared with control subjects, had (1) a higher prevalence of work-related respiratory symptoms (p less than 0.05) and significant decrements in forced-expiratory volume in one second (FEV1) and maximal flow rates after exhalation 50 and 75% of forced vital capacity (Vmax50 and Vmax75) during the work shift, and (2) significant differences (p less than 0.05) in preshift/postshift percent changes in forced vital capacity (FVC), Vmax50 and Vmax75. Adjusting for age, height, and smoking habit, grain handling still had a significant negative effect on FVC, Vmax50, and Vmax75. In grain workers, we found a significant (p less than 0.05) negative relationship between total dust levels and the percent change in FVC, Vmax50, and Vmax75 and a positive relationship between dust level and percent change in leukocyte counts. Grain workers' perception of dust level correlated with the measured dust level and the prevalence of symptoms. Occupational exposure to grain dust during a work shift has a dose-related adverse acute respiratory effect regardless of smoking habit, atopic status, or age, and it produces a dose-related leukocyte response at total dust levels below 15 mg/m3.