The clinical applications of SPECT are just beginning to be defined since complete systems have only recently become available. SPECT studies are more difficult to perform than planar imaging studies, and close attention to quality control is important to obtain optimal studies. SPECT has higher lesion contrast and is able to detect smaller lesions than planar imaging in Tc-99m sulfur colloid liver studies. Preliminary results of SPECT T1-201 studies are encouraging, but further work comparing SPECT and planar imaging of T1-201 is needed. SPECT does give more information than planar imaging in certain bone imaging cases such as suspected avascular necrosis of the hip. Although interesting results have been published using SPECT in brain and lung perfusion studies, the clinical utility of this work has not been determined. The development of certain radiopharmaceuticals would enhance the future of SPECT. Technetium-99m labeled brain and myocardial perfusion agents would be ideally suited for SPECT studies. The ability to quantitate lesion volume (eg, in liver metastases) has not been studied and could be useful in following patents on chemotherapy. SPECT could give additional information if monoclonal antibodies labeled with I-123 or Tc-99m can be demonstrated to have appropriate sensitivity. The advantages of SPECT over planar imaging will be greater as new agents are developed.