The lung function of 163 middle-aged military officers was studied in relation to smoking habits. The 113 habitual cigarette smokers were found to have significantly lower average ventilatory capacities and increased residual volumes as compared with 50 nonsmokers. Although most subjects in both groups were within normal range, there were significantly more smokers who demonstrated abnormal results to tests of maximum voluntary ventilation, timed vital capacity, and residual volume. Habitual smokers also admitted to chronic cough and shortness of breath with greater frequency than did nonsmokers, although the differences were not statistically significant. The authors conclude that these differences cannot be explained on any factor other than that one group smoked and the other group did not.