Early diagnosis of infection in the immunocompromised patient is often difficult because of an impaired inflammatory response to microbial invasion. Radioscintigraphy has certain advantages in approaching this problem: because it is based upon either delivery of leukocytes to the site of infection or the leakiness of capillaries to radiolabeled proteins, earlier diagnosis is possible, even in patients with surgically altered anatomy; whole-body imaging allows the detection of focal sites of infection that are unsuspected clinically; and the semiquantitative nature of the information obtained allows for serial studies to assess the response to therapy. Three reagents are either currently available (gallium-67 citrate and radiolabeled leukocytes) or soon to be available (indium-111-labeled nonspecific polyclonal IgG) for this purpose. A major disadvantage of all three techniques is that a delay of 18-24 hours between injection and imaging is required. Experimental reagents such as technetium-99m-labeled chemotactic peptides appear to require < 3 hours between injection and imaging.