The relationship of eosinophilia with smoking habits and with baseline lung function measurements has been studied in a working population of 912 men in the Paris area. Absolute numbers of eosinophils were related significantly to a history of asthma and eczema in childhood as well as to current tobacco consumption, whereas the percentage of eosinophils was related only to the occurrence of asthma and eczema. Forced expiratory volume in one second adjusted for smoking was significantly related to asthma, the presence of a common cold on the day of examination among those with a history of wheezing, and the percentage of eosinophils. The association between FEV and eosinophils was restricted to never smokers. Among never smokers without a history of asthma, eczema, wheezing, or a common cold on the day of examination, eosinophil percentages and counts were significantly associated with the level of FEV; eosinophil percentages explained 4.4% of the variance of FEV. These results suggest that eosinophilia might be a risk factor for chronic air-flow limitation among adult nonsmokers.