Purpose: Purpose of this study is to synthesize 99mTc-labeled transferrin for infection imaging and to compare it with 67Ga-citrate for the detection of infectious foci. Materials and methods: Succinimidyl 6-hydrazino-nicotinate hydrochloride-chitosan-transferrin (Transferrin) was synthesized and radiolabeled with 99mTc. Labeling efficiencies of 99mTc-Transferrin were determined at 10 min, 30 min, 1 hr, 2 hr, 4 hr and 8 hr. Biodistribution and imaging studies with 99mTc-Transferrin and 67Ga-citrate were performed in a rat abscess model induced with approximately 2¡¿108 colony forming unit of Staphylococcus aureus ATCC 25923. Results: Successful synthesis of Transferrin was confirmed by mass spectrometry. Labeling efficiency of 99mTc-Transferrin was 96.2¡¾0.7%, 96.4¡¾0.5%, 96.6¡¾1.0%, 96.9¡¾0.5%, 97.0¡¾0.7% and 95.5¡¾0.7% at 10 min, 30 min, 1 hr, 2 hr, 4 hr and 8 hr, respectively. The injected dose per tissue gram of 99mTc-Transferrin was 0.18¡¾0.01 and 0.18¡¾0.01 in the lesion and 0.05¡¾0.01 and 0.04¡¾0.01 in the normal muscle, and lesion-to-normal muscle uptake ratio was 3.7¡¾0.6 and 4.7¡¾0.4 at 30 min and 3hr, respectively. On image, lesion-to-background ratio of 99mTc-Transferrin was 2.18¡¾0.03, 2.56¡¾0.11, 3.08¡¾0.18, 3.77¡¾0.17, 4.70¡¾0.45 and 5.59¡¾0.40 at 10 min, 30 min, 1 hr, 2 hr, 4 hr and 10 hr and those of 67Ga-citrate was 3.06¡¾0.84, 4.12¡¾0.54 and 4.55¡¾0.74 at 2 hr, 24 hr and 48 hr, respectively. Conclusion: Transferrin is successfully labeled with 99mTc, and its labeling efficiency was higher than 95% and stable for 8 hours. 99mTc-Transferrin scintigraphy showed higher image quality in shorter time compared to 67Ga-citrate image. 99mTc-transferrin is supposed to be useful in the detection of the infectious foci. (Nucl Med Mol Imaging 2006;40(3):177-185)