The pattern of cigarette smoke inhalation was studied in 19 smokers with respiratory inductive plethysmography, a reliable unobtrusive ventilatory monitoring device. The mean volumes inhaled varied widely from 0.27 to 1.97 L, with a group mean (+/- SD) of 0.79 +/- 0.45 L. Mean duration of smoke inhalation varied from 2.0 to 6.8 seconds, with a group mean of 4.5 +/- 1.3 seconds. An inhalation fraction was derived by dividing the inhaled volume by the vital capacity; this fraction varied from 0.09 to 0.47, with a group mean of 0.20 +/- 0.10. Subjects rated the depth that they inhaled smoke into their lungs on a visual analog scale and on a grading system. Correlation between visual analog scale and inhalation fraction was poor (r = -0.15). Also, inhalation fraction bore no relationship to smoking pack-years or current pulmonary function. The smokers' inaccurate assessment of their inhalation pattern may help to explain the poor correlation reported between cigarette smoke inhalation and severity of obstructive lung disease.