Twenty-six of 43 patients (60.5%) with classic rheumatoid arthritis (RA) participating in a controlled, prospective study were found to have maximal midexpiratory flow rates (MMEFs) suggestive of obstructive pulmonary disease. Cigarette smokers with RA had significantly lower MMEFs than either nonsmokers with RA or smokers with degenerative joint disease. There was an increased prevalence of the Pi phenotype MS among the RA patients. Interstitial fibrosis, tobacco smoking, and protease inhibitor deficiencies were all significant factors in producing airway obstruction in patients with RA.