Bronchoalveolar lavage (BAL) is frequently performed in patients with suspected ocular sarcoidosis. This study describes the immunogenetical, immunological, radiological, and functional features of a subclinical alveolar lymphocytosis unrelated to sarcoidosis in patients with chronic uveitis. Two hundred and ten patients with chronic uveitis of unknown origin, who underwent fiber-optic bronchoscopy with BAL as part of a prospective protocol over a three-year period, were evaluable for retrospective analysis. Sixty-five patients had alveolar lymphocytosis: Sarcoidosis was diagnosed in 13 (6%) patients, whereas alveolar lymphocytosis was considered unrelated to sarcoidosis in 52 (25%). Alveolar lymphocytosis unrelated to sarcoidosis was not associated with radiologically detectable interstitial lung disease or pulmonary function impairment. CD4/CD8 lymphocyte ratio was 3.7 +/- 3.0. Total cell count, total lymphocyte, and CD4 lymphocyte percentage were significantly lower when compared with sarcoidosis-related alveolitis (129,000 +/- 80,000 vs. 218,000 +/- 117,000, p <0.05; 33.1% +/- 13.2 vs. 39.7% +/- 13.2, p <0.05; and 54.3% +/- 18.2 vs. 65.4% +/- 10.1, p <0.05, respectively). Patients with alveolar lymphocytosis unrelated to sarcoidosis were older (47.8 +/- 17.7 years vs. 42.7 +/- 14.2 years, p <0.05) and more likely to carry the HLA-B51 allele (19.7% vs. 7.1%, p <0.01) than patients with chronic uveitis without alveolar lymphocytosis. They did not appear to be at risk of developing clinically apparent interstitial lung disease on followup. We conclude that alveolar lymphocytosis is frequently observed in patients with chronic uveitis. It is generally unrelated to sarcoidosis and may then be associated with a distinctive immunogenetic phenotype.