Advances in medical imaging for cancer diagnosis and treatment. Over the last several decades, significant "new eyes" have been developed that improve the diagnosis, treatment, planning, and monitoring of human cancer: computer tomography (CT), magnetic resonance imaging (MRI) and spectroscopy (MRS), single photon emission computed tomography (SPECT), and positron emission tomography (PET). Innovative advances in both morphologic and functional imaging have led to a dramatic improvement in our ability to diagnose and monitor human cancer. Frequently, anatomic detail can be demonstrated in ways that exceed views at surgery, and functional biochemical imaging is being used to show the metabolic activity and receptor status of normal and pathologic states. In vivo functional and biochemical studies differentiate normal from neoplastic or nonviable tissue, and make it possible to measure progression or regression of the disease. Because physiologic changes often precede morphologic findings in many disease processes, the use of in vivo biochemical probes can demonstrate disease before anatomic abnormalities become evident. Gross changes in anatomy are no longer adequate endpoints for therapy protocols. Today, using physiologic imaging, we can evaluate the response to treatment within hours of administration of therapy. Adjuvant metabolic tumor imaging studies provide complimentary information to morphologic evaluation of human cancers that will ultimately lead to better patient care. 