Respiratory symptoms and abnormal findings on chest X-ray are frequently noted in patients with chronic lymphocytic leukemia (CLL). However, most of these represent pulmonary infections or mediastinal lymphadenopathy, and leukemic involvement of the lung is seldom diagnosed during life. In this report we describe three patients with non-progressive, responsive CLL who developed biopsy proven pulmonary infiltration with CLL. In one case, pulmonary involvement was the sole manifestation of recurrent disease and a second case had little disease elsewhere with minimal CLL in the blood at the time pulmonary involvement appeared. In all three cases, transbronchial biopsy and bronchoalveolar lavage performed during fibreoptic bronchoscopy provided adequate tissue for diagnosis. We conclude that CLL may involve the lung even in the presence of a low peripheral white blood cell count with responsive disease elsewhere, and can readily be diagnosed by transbronchial biopsy and bronchoalveolar lavage.