The ocular manifestation of human T-cell lymphotropic virus type I (HTLV-I) infection has been recognized as a new clinical entity termed HTLV-I uveitis. In order to determine whether HTLV-I uveitis is associated with lymphocyte alveolitis, bronchoalveolar lavage (BAL) was carried out in 11 patients with HTLV-I uveitis, five asymptomatic HTLV-I carriers, 11 HTLV-I-negative patients with ocular sarcoidosis, and nine normal control subjects seronegative for HTLV-I. Six of the 11 patients with HTLV-I uveitis showed increased total cell counts, and T-lymphocytosis in BAL fluid. CD4+/CD8+ ratios of T-lymphocytes were decreased in three of these patients, and normal in three other patients. Such abnormalities of the lung were not found in asymptomatic HTLV-I carriers, and in normal control subjects. BAL findings in HTLV-I uveitis differed from those of patients with sarcoidosis in terms of the lymphocytic component. Interestingly, it was found that there was an increase of HTLV-I proviral deoxyribonucleic acid (DNA) load in peripheral blood mononuclear cells (PBMC) from seven patients with HTLV-I uveitis, and in the BAL cells from four patients with pulmonary involvement. These results provide further evidence in terms of HTLV-I tropism for the lung, and suggest that a systemic and local increase of HTLV-I proviral DNA load plays an important role in the pathogenesis of lymphocyte alveolitis in patients with HTLV-I uveitis.