Relations between blood pressure and cigarette smoking were investigated on the basis of a health survey conducted in a population of 3034 mine workers from Quebec Province. Blood pressure was found to be lower among smokers than among non-smokers, the difference between these two groups being: systolic pressure 2.3 mmHg, diastolic pressure 3.0 mmHg. After adjustment for age and bodyweight this relation persisted but only as far as diastolic pressure was concerned. The prevalence of hypertension was 1.5 times higher in non-smokers than in smokers. On the other hand, the number of cigarette-smoking years and the number of cigarettes smoked per day seemed to have little effect on mean arterial pressure.