To evaluate respiratory risk in dairy farmers, the present authors conducted a longitudinal study in the Doubs region of France. From a cohort constituted in 1986 (T1), 157 (62.8%) dairy farmers and 159 (63.6%) controls were re-evaluated in 1998 (T3). The study protocol comprised a medical and occupational questionnaire, spirometric tests at both evaluations, and noninvasive measure of blood oxygen saturation with pulse oximetry (S(p,O(2))) at T3. In 1998, the prevalence of chronic bronchitis was higher in dairy farmers. In cross-sectional analyses, all respiratory function parameters and S(p,O(2)) were significantly lower in dairy farmers. In a multiple linear regression model, farming, age, male sex and smoking were significantly and negatively correlated with S(p,O(2)). However, the mean annual decline in respiratory function parameters did not differ significantly between groups. After adjustment of covariables, accelerated decline in vital capacity and forced expiratory volume in one second was associated with age, smoking and male sex. Decline in vital capacity was accelerated in dairy farmers working in traditional farms and those currently foddering. The current study demonstrates that dairy farming is associated with an increased risk of lung disorders and a decrease in blood oxygen saturation and suggests that respiratory function impairment is correlated with cumulated exposure to organic dusts.