The effectiveness of CT scanning in radiotherapeutic treatment planning was evaluated in 32 patients with bronchogenic carcinoma. CT of the chest in pretreatment evaluation of these patients supplemented conventional clinical and radiographic patients supplemented conventional clinical and radiographic studies, resulting in (1) more clear delineation of tumor extent in 24 patients (75%); (2) change in assessment of the size of lesions in 14 patients (43%); (3) change of disease stage in 13 (40%); (4) demonstration of inadequacy of treatment plan in nine (28%); and (5) changes in the volume of normal tissue irradiated in 14 (40%). CT scan data was judged essential for treatment planning in 17 patients studied (53%). Unsuspected areas of tumor involvement were seen in 21 patients (65%). Use of the CT scan as a patient contour for radiotherapy treatment planning of lung cancer and alternative techniques are discussed.