In a retrospective study of 81 patients with non-Hodgkins's lymphoma and 35 patients with chronic lymphatic leukaemia, pulmonary involvement was found in 25% of cases and pleural effusion in 19%. Twenty-four patients (20%) had intrathoracic lymphadenopathy and 12 of these had associated pleural or lung involvement. Infiltration occurred almost exclusively in diffuse lymphocytic lymphoma and chronic lymphatic leukaemia, whereas round lesions were seen only in undifferentiated lymphomas. Pleural effusion complicated most histological types of non-Hodgkin's lymphoma but was uncommon in chronic lymphatic leukaemia. Pleural biopsy was successful in diagnosing lymphoma in nine of ten patients with an effusion in whom it was performed. Both pulmonary and pleural involvement responded poorly to treatment and had an adverse effect on prognosis. In contrast, intrathoracic lymphadenopathy responded well to radiotherapy and/or chemotherapy and did not affect prognosis adversely when it occurred in the absence of other intrathoracic manifestations of lymphoma.