Studies of lung function in 3 patients with symptomatic secondary pulmonary lymphoma (2 with Hodgkin's disease and one with lymphoblastic lymphoma) showed an interstitial pattern of dysfunction. The lymphomatous infiltration and associated nonspecific patchy interstitial fibrotic lesions seen at autopsy and on biopsy specimens were extensive enough to account for the decrease in lung volumes, low carbon monoxide diffusing capacity, hypoxemia, and hyperventilation.