Computed tomography (CT) examinations of the chest were evaluated in 100 patients treated with bleomycin. The CT findings were compared with those of conventional chest radiographs and lung-function tests. Lung damage due to bleomycin was detected in 38% of patients by CT, while damage was detected in only 15% by radiography. Changes in appearance seen on CT scans due to bleomycin damage were compared with measurements of lung volume and gas transfer per unit lung volume. There was good correlation between severity of damage shown on CT scans and changes in lung volume (P less than 0.01). Gas transfer capabilities were reduced in most patients regardless of changes observed on CT scans. Sequential CT studies showed that complete resolution of bleomycin damage may occur within 9 months in patients with minor or moderate damage. Residual abnormalities were seen in all patients with severe damage. CT can confirm lung damage in a patient with suspected toxicity but a normal chest radiograph and can define the anatomic extent of disease in a patient with an abnormal lung-function test.