Motivation for smoking cessation benefits from physician counseling. To further improve this educational process, spirometry can demonstrate ventilatory impairment to the smoker. In addition to comparing a person's spirometric results with predicted reference values for normal subjects, estimation of "lung age" can be used to demonstrate the effects of cigarette smoking. Equations were developed from reference linear regression equations permitting lung age estimation in terms of ventilatory function. This age can then be compared with the individual's chronological lung age. Normal and abnormal groups determined by a respiratory health questionnaire and pulmonary function testing were used to compare the value of single and combination spirometric tests. The forced expiratory volume at 1 sec proved superior to any other single test or combination for best separation of the two groups and had the lowest standard error for estimated lung age. Both spirometry and estimated lung age calculation may be useful for motivating cessation of cigarette smoking.