For imaging inflammation, white cells can be labelled with In-111 tropolonate or Tc-99m HMPAO, both of which are lipophilic complexes capable of penetrating etrating cell membranes. Mixed white cells are satisfactory for routine clinical use although in some circumstances, such as for quantitative studies, pure granulocytes are preferable. The normal distribution of labelled leukocytes includes the spleen, liver, bone marrow and lung. Although the extent of pulmonary uptake reflects labelling injury, it also reflects, with different kinetics, increased intravascular granulocyte transit time, which is encountered in several systemic inflammatory diseases. The clinical applications of labelled white cells include imaging soft tissue sepsis, imaging and quantification of inflammatory bowel disease and diagnosis of osteomyelitis. New agents for imaging inflammation are designed, in general, to target inflammationin vivo without the need for blood cell isolationin vitro. They include non-specific immunoglobulin (HIG) and monoclonal antibodies (mAbs) to granulocytes. mAbs to endothelium are also being developed but have not yet been tested in man.