The relation of ventilatory function to overall mortality has been studied in 662 male and 2048 female never-smokers who during the period 1976-1978 participated in the Copenhagen City Heart Study, a prospective community study of more than 14,000 men and women randomly selected from the general population of the City of Copenhagen. Until the end of 1986, 195 subjects who said they were never-smokers died. Mortality was analyzed using the proportional hazards model of Cox. In addition to measures of ventilatory function, the mortality analysis included age, sex, body-mass index, alcohol consumption, school education, diabetes mellitus, heart disease and bronchial asthma as confounding factors. Forced expiratory volume in 1 second (FEV1) as a percentage of that predicted, forced vital capacity (FVC) as a percentage of that predicted and the ratio of FEV1 to FVC were significant risk factors for mortality among both sexes. The relative risk of death associated with a 50% decrease in FEV1 and FVC as a percentage of a predicted value was 1.65 and 1.81, respectively. This study confirms that lowered ventilatory function is a strong risk factor for mortality among never-smokers of both sexes.