Of a random sample of farmers in two crop districts of Manitoba mailed a respiratory questionnaire in 1976, 833 (82% of those currently farming in the area) replied. More than half were grain farmers and nearly half had never smoked cigarettes. The prevalence of chronic cough and phlegm production, wheezing and exertional dyspnea was positively related to the amount of smoking but was also higher than expected in nonsmokers. Acute dyspnea, sometimes of delayed onset and accompanied by fever, was most commonly related to handling old grain and was reported by 44% of the farmers. Current smokers were more susceptible than nonsmokers to this type of dyspnea. Farmers with history of acute dyspnea while handling grain were more likely to wear masks, but the overall rate of mask wearing, even among those at highest risk, was low.