One hundred nonsmoking patients with rheumatoid arthritis, including 63 with rheumatoid arthritis alone (RA group) and 37 who also had secondary Sjögren's syndrome (sSS group), underwent a detailed evaluation of their pulmonary function. The results were compared with those of 110 age-matched nonsmoking controls. Normal function was significantly less common in both patient groups than in the controls. A significant percentage of patients had small airways disease (SAD) which was observed with similar frequency in the control group. If this were excluded, then isolated impairment of carbon monoxide diffusing lung capacity (DLCO) was the most commonly detected significant abnormality in both patient groups. Restrictive disease was following in frequency in the RA group, but was absent in the sSS group. Obstructive disease was very uncommon in all of the patients. In general, there were no significant differences in the frequency of the various respiratory function abnormalities between patients with RA only and those with concomitant sSS, whereas between patients and controls, the only statistically significant differences were the higher frequencies of isolated DLCO impairment and restrictive disease in the RA group.