The purpose of this study is to investigate the ability of I-131 labeled polyclonal human immunoglobulin to localize an infection. In our country, indium-111 labeled leukocyte or Tc-99m labeled IgG are not readily available because of compex, time-consuming procedure and cost. So we tried to localize infection with I-131 labeled IgG which could be easily prepared. Six rats, infected with staphylococcus aureus in a thigh muscle, received I-131 labeled IgG intravenously and I-131 labeled bovine serum albumin (BSA) were injected to other 5 infected rats. Scintigrams were made at 1, 4, 24, 48, 72 hour later. The radiopharmaceutical demonstrated significant accumulation at the site of infection. The accumulation of I-131 labeled IgG at the site of infection was significantly (P<0.05) higher than that of I-131 labeled BSA at 48, 72 hour. Similar finding could be found at 24 hour imaging, but it was not significant statistically. Therefore it was found that vascular permeability alone could not account for the mode of action of I-131 labeled IgG and it was considered that specific binding played a role. In conclusion, focal sites of inflammation can be detected with I-131 labeled nonspecific human polyclonal IgG and it seems that this method can also be applied to localization of human infection.