Technetium (99mTc) labelled, polyclonal human immunoglobulin (HIG) is a new agent that detects focal infection and inflammation. This new agent was compared in 40 patients with the accepted standard, namely 111In-oxine-labelled leucocytes. This comparison resulted in a sensitivity of 94% and a specificity of 96% for 99mTc-HIG when 111In-oxine leucocytes were defined as giving the true result. The new agent was shown to localize both sepsis and active inflammatory bowel disease (IBD). There was 100% concordance in the 16 patients with IBD who were imaged with both 99mTc-HIG and 111In-oxine leucocytes. Discordant results were obtained in one case of suspected osteomyelitis, which was false-positive on the 99mTc-HIG scan, and one case of pyrexia of unknown origin when the 99mTc-HIG was false-negative and the 111In-oxine leucocyte scan demonstrated accumulation of tracer in the caecum at 24 h post-injection. Normal distribution for 99mTc-HIG demonstrated activity in the kidneys and bladder and that 50% of the tracer is cleared through the kidneys during the first 24 h post-injection. There were no major or minor side-effects.