In this experimental study, the utility of Tc-99(m)-polyclonal human immunoglobulin (Tc-99(m)-HIG) for localizing acute and chronic phases of inflammatory lesions was investigated. Three groups of rats were inoculated with Staphylococcus aureus in the right thigh. Then, 24 h (group I, n = 12), 48 h (group II, n = 12) and 72 h (group Ill, n = 12) post-inoculation, the rats received 40 MBq Tc-99(m)-HIG into the jugular vein. In addition, two control rats were studied at 24 h after inoculation of sterile saline. Both visual and quantitative evaluations were undertaken. The acute and chronic stages of inflammation were determined by pathological examination. The mean (+/- S.D.) lesion/contralateral uptake ratios at 4 and 24 h after Tc-99(m)-HIG injection were: group I, 1.22 +/- 0.1 and 2.12 +/- 0.16; group Il, 1.15 +/- 0.08 and 2.25 +/- 0.16; group III, 1.06 +/- 0.09 and 2.08 +/- 0.14. In conclusion, the acute and chronic phases of infection showed non-significant differences in Tc-99(m)-HIG uptake ratios.