OBJECTIVE: A longitudinal evaluation of lung involvement in primary Sjögren's syndrome (SS). METHODS: Eighteen non-smoking women fulfilling the European criteria for primary SS were followed for 55 months (range 26-137 mos.). These were consecutive patients with exclusion for current smokers and patients with lung diseases. Every patient underwent clinical examination, chest radiographs and lung function tests (spirography, flow/volume loop and CO lung diffusing capacity measurements). No patient was given any immunosuppressive or mucolytic therapy. RESULTS: Cough, dyspnea on exertion and recurrent bronchitis were observed in 50, 40 and 20% of the patients respectively and their frequency did not change with time. Chest radiographs were and remained normal. At presentation, lung volumes and diffusing capacity were in the normal range, whereas expiratory flows in the small airways tended to be in the low range. With time, the peak expiratory flow (PEF) significantly increased (95.8 +/- 4.6 v 103.5 +/- 4.6, mean +/- SE, % of predicted, Wilcoxon, p < 0.05) whereas the lung transfer factor for CO (TLCO) and the transfer coefficient (KCO = TLCO/alveolar volume) decreased (92.9 +/- 4.0 v 87.0 +/- 4.0 and 89.7 +/- 2.4 v 84.2 +/- 2.6 respectively, p < 0.05 for both). The TLCO decrease, corrected for the duration of follow-up, correlated with the titers of IgA circulating immune complexes (CIC) at presentation and to a lesser extent with the occurrence of cough. CONCLUSION: During the follow-up of these primary SS patients, respiratory symptoms did not change, the recurrent respiratory infection rate was low, and no cases of pulmonary hypertension or lymphoma was observed. The diffusion capacity decrease was associated with IgA CIC titers at presentation. This impairment could contribute to dyspnea during its evolution over a lifetime but is too slight to explain the dyspnea on exertion seen in most of our patients.