This study sought to determine which blood component, WBCs or platelets, is the more specific indicator of an abscess and where each localizes. An abscess was created using stool in the hind limb of dogs. After 24 hours, one group was given autologous indium 111-labeled platelets and another group was given autologous indium 111-labeled WBCs. Blood, abscess fluid, infected operative control muscle tissue, and nonoperative control muscle tissue were counted for radioactivity 24 hours after administration of the labeled cells. There was significantly (P less than .001) less WBC radioactivity in blood and more within abscess fluid compared with platelets. The highest platelet activity occurred in muscle tissue adjacent to the abscess (P less than .002) compared with platelet activity in abscess fluid or control muscle tissue. The unwanted high platelet blood background activity and the desirable high concentration of WBC radioactivity within the abscess fluid makes the latter the preferential radionuclide imaging agent.