The ability to fuse (or merge) data sets from SPECT and coincidence nuclear medicine scans with computed tomographic images combines physiologic information from the former method with the superior anatomic resolution of the latter technique. In many cases, this allows more definitive diagnosis than can be obtained by simple visual comparison of nuclear medicine images and conventional cross-sectional imaging. The technique may be used in the staging and follow-up of lung carcinoma, pulmonary carcinoid, and lymphoma. It may also aid in the interpretation of perfusion defects in Tc-99m MAA lung scanning, aid in the interpretation of ground-glass opacity in selected cases of chest high-resolution computed tomography, and aid in the diagnosis of some mediastinal masses (e.g., intrathoracic goiters). In this nuclear medicine atlas, the method used to create fusion images in the chest is described, and examples of fusion imaging with radiopharmaceuticals are given that may be of clinical use in chest disease.