The reliability of the preoperative CT diagnosis was studied in patients with pulmonary metastases from osteosarcoma and colorectal cancer as compared with surgical and pathological findings. Seventy-six lesions among 111 surgically proven metastatic nodules were detected preoperatively by CT. But the predictive rate varied greatly depending upon the site and size of the lesions. CT is not so useful in subpleural and apical sites or with nodules of less than 0.2 cm in diameter.