A study of work shift changes in pulmonary function in unexposed blue collar workers was conducted. The cohort consisted of 944 blue collar employees, mean age 33 years, at 35 work sites at beverage bottling facilities, food preparation and packaging factories, assembly factories, parks, and nurseries in the southern United States. Subjects were judged to have no hazardous occupational respiratory exposures on the basis of site visits and industrial hygiene monitoring. The subjects completed a questionnaire to obtain information on demographic characteristics, respiratory symptoms, smoking habits, and occupational history. Pulmonary function testing was performed before and after an 8 hour work shift. Approximately 90% of the subjects were male. The approximate racial composition of the cohort was white 30%, black 45%, and Hispanic 25%. The overall mean preshift values of 1 second forced expiratory volume (FEV1), forced vital capacity (FVC), and peak expiratory flow (PEFR) were 3.69 liters (l), 4.55 and 9.56 liters/second (l/sec), respectively. The overall mean shift changes in FEV1 and PEFR were (-)0.04l and 0.13l/sec. Across shift changes in FEV1 and PEFR were not significantly related to age, sex, race, smoking habits, work shift, or FEV1/FVC ratio. The standard deviations in across shift changes in FEV1 were smaller for younger workers, white workers, never smokers, day shift workers, and for workers with normal FEV1/FVC ratios. The standard deviations of shift related changes in PEFR were smaller for younger workers, male workers, white workers, and for workers with normal FEV1/FVC ratios. The authors conclude that the data should be useful for occupational respiratory morbidity studies that are based on across shift changes in FEV1 and PEFR.