This is a support and development project related to several Clinical Protocols at the National Institutes of Health. Thirty to 50 percent of the patients studied by the Nuclear Medicine Department have benign or malignant tumors. Detection and localization of these tumors is important for surgical removal, for staging, and for assessing the effects of chemotherapy. Because Nuclear Medicine imaging is based on metabolic, biochemical, or vascular characteristics of tumors, its results are complementary to imaging procedures based on anatomy. Usually, Nuclear Medicine imaging is more sensitive for tumor detection than computer tomography (CT) or magnetic resonance imaging (MRI), but the Nuclear Medicine images often do not show adjacent tissues or organs, so the abnormality is imprecisely located. For optimal clinical care, Nuclear Medicine findings must often be correlated with CT or MRI images. Generally, this correlation is done at clinical conferences, but as new tumor localization radiopharmaceuticals are being developed, the department and section are working at electronically fusing tomographic Nuclear Medicine images with CT or MRI. Specific protocols where fusion of images may be important for clinical care include In-111 octreotide imaging of gastrinoma and other neuroendocrine tumors, Tc-99m sestamibi imaging of parathyroid tumors, and I-131 or I-123 MIBG imaging of pheochromocytoma. Nuclear Medicine also supports cancer therapy research by performing functional studies including: 1.) I-131 dosimetry of thyroid cancer; 2.) Tc-99m sestamibi imaging of p-glycoprotein activity which is related to the multidrug resistance gene; and 3.) In-111 labeled tumor seeking lymphocytes imaging. The department uses technology assessment methodology (receiver operating characteristics curve analysis, etc.) to evaluate the utility of various imaging procedures.