In this study of a general population sample, highly significant quantitative relationships were noted between pack-years of smoking and functional impairment. Subjects with chronic productive cough showed steeper declines in the forced expired volume in 1 sec and forced expiratory flow after exhalation of 75 per cent of the forced vital capacity (Vmax 25), but a definite inverse relationship between ventilatory function and pack-years was demonstrated even among subjects who denied any cough or sputum production. Current smoking showed no relationship to 1-sec forced expiratory volume or Vmax 25 when total pack-years were taken into account. Age appeared to be an important independent determinant of per cent predicted values only in regard to the Vmax 25 in symptomatic nonsmoking women. A history of childhood respiratory trouble was associated with a lower ventilatory function regardless of smoking habits, and for this reason such subjects have been deleted from detailed analyses of dose-effect relationships. Allergy skin test reactivity in young to middle-aged adults showed a significant additive effect to pack-years as a determinant of forced expiratory flow toward the end of the forced vital capacity, but the effect was noted only among present smokers.