The aim of this study was to assess the role of 131 I-L-tyrosine for diagnosing E. coli infection and differentiating the infection from the inflammary lesion in mice. The L-tyrosine was labeled with 125 I by N-bromosuccinimide. The binding rates of 125 I-L-tyrosine with E. coli were tested by culturing E. coli with 125 I-L-tyrosine in poor nitrogen yeast medium and in rich nitrogen LB medium separately. The bio-distribution of 125 I-L-tyrosine and the 131 I-L-tyrosine SPECT scintigraphy in E. coli infection of mice were studied separately. The results revealed that the label rate of 125 I-L-tyrosine was more than 99%. The percentage of 125 I-L-tyrosine binding with E. coli was 2.78% in yeast medium, and was 0.85% in LB medium. The distribution peak of 125 I-L-tyrosine in E. coli focal infection of mice was in the range between 45 and 60 min. The infection/normal muscle ratio was 2.46 after 60 minutes. The SPECT scintigraphy demonstrated an accumulation of the 131 I-L-tyrosine in the E. coli focal infection during the 45-60 minutes. The infection/normal muscle ratio of the 131 I-L-tyrosine radioactivity was 2.51 in infectious mouse. However, the SPECT scintigraphy also demonstrated an accumulation of the 131 I-L-tyrosine in the inflammatory lesion during the 45-60 minutes. The lesion/normal muscle ratio of the 131 I-L-tyrosine radioactivity was 2.29 in inflammatory mouse at 60 mins. Thus, the 131 I-L-tyrosine SPECT scintigraphy could diagnose the E. coli infection, but it can not be used for differentiating the bacteria infection and the inflammatory lesion in mice. Our study revealed that the 131 I-L-tyrosine would play a potential role in diagnosing the inflammatory lesion in human beings.