Objective To investigate the biodistribution and gamma imaging of 99Tcm-arginine-glutamate-threonine (RET) in nude mice bearing lung cancer xenografts and to explore its feasibility for human lung cancer imaging.Methods RET was labeled directly with 99Tcm.The binding efficiency of 99Tcm-RET with human NSCLC H1299 cells was measured.99Tcm-RET was injected via the tail vein in nude mice bearing H1299 xenografts.The mice(n=32) were sacrificed at different time points:15 min,30 min,1 h,2 h,4 h,8 h,24 h,and 48 h.Organs of interest were excised,weighted and counted by a gamma counter.The organ uptake was calculated as ％ID/g.The gamma imaging was performed on 3 mice at 0.5,1,2,4,4.5,5,6 h after intravenous injection of 4.81 MBq 99Tcm-RET.Results The radiolabeling yield of 99Tcm-RET was (93.15±2.02)％,and the binding efficiency of 99Tcm-RET with H1299 cells was (3.56±0.37)％.At 4 h after injection,the uptake of tumor,liver and spleen was (4.96±1.05) ％ID/g,(15.89±1.84) ％ID/g and (10.83±1.66) ％ID/g and the T/NT was 5.70±0.21 for the heart and 12.40±0.11 for the blood.The tumor in nude mice could be best visualized at 4.5-6.0 h.Conclusion 99Tcm-RET might have potential to serve as a lung cancer imaging agent.