The role of gallium imaging in infection has changed considerably during the past several years. Once the mainstay of radionuclide imaging of infection, it has been supplanted to a very great extent by labeled leukocyte imaging. Despite the success of the labeled white-cell technique, gallium still plays an important role in the radionuclide evaluation of infection. It is not possible, for a variety of reasons, to perform white-cell imaging on all patients, and gallium imaging is certainly an acceptable substitute. In certain circumstances, rather than merely being a substitute, gallium is an important complement to leukocyte imaging. This is best illustrated by the patient with a fever of unknown origin (FUO). Although a negative leukocyte study effectively excludes an acute infection, it fails to identify the source of the patient's fever, a not uncommon situation in view of the fact that only approximately 25% of all FUOs are caused by infection. A complementary gallium study under these circumstances may identify either a chronic infectious process or even a neoplasm, conditions for which white-cell imaging is relatively insensitive. Although leukocyte imaging is probably superior to gallium for most infections of the musculoskeletal system, this technique is of limited value in patients with suspected vertebral osteomyelitis. There are data that suggest that sequential bone gallium imaging may be a better way to diagnose this entity. Finally, in immunocompromised patients, gallium imaging is clearly the procedure of choice for detecting the opportunistic respiratory infections and lymph node abnormalities that are so prevalent in this population.