The severe immunologic alterations caused by HIV infection is at the base of respiratory tract infections, neoplasms and inflammatory complications which represent the most frequent cause of death in AIDS patients. The etiological diagnosis is difficult and often needs invasive procedures. Among those, BAL is surely the most useful method because of its lesser invasiveness and better tolerability and more for its sensibility and easier repeatability. Besides the etiological evaluation of lung infections, BAL allows to obtain and analyze immunologic and inflammatory cells from alveolar spaces consenting the acquisition of data regarding immunopathogenetic mechanisms related to pulmonary complications during AIDS. We report data about cytoimmunologic study of BAL fluid in 10 patients of ours.