Radiolabelled human immunoglobulin (HIG) scintigraphy has been recognized as a reliable modality for the localization and evaluation of pyogenic infection in humans. Four methods of labelling HIG with 99Tcm developed by the Institute of Nuclear Energy Research of Taiwan are: (1) using ascorbic acid (ASC) for direct labelling of HIG (ASC-HIG); (2) using diethylenetriamine pentaacetate (DTPA) as a bifunctional chelate (DTPA-HIG); (3) using 2-iminothiolane (IM) for modified protein (IM-HIG); (4) using the avidin-biotin system (AVI-BIO-HIG). Our study assessed these four preparations in the scintigraphic detection of infections. Staphylococcus aureus was injected intramuscularly into the left thighs of rabbits. Two days later, when active inflammation developed, 5 mCi 99Tcm-HIG was given intravenously; scintigraphy was performed at 1, 4 and 18 h. The accumulation of 99Tcm DTPA-HIG was the most prominent among the four preparations at the site of infection. It is concluded that 99Tcm labelling of HIG using DTPA as a bifunctional chelate may be the optimal labelling method for detecting infection.