The validity of 99mTc-YIGSR,a novel receptor radio-tracer,in imaging the Ehrlich ascites tumor was evaluated.YIGSR,a pentapeptide of laminin,was labeled with 99mTc by using a bifunc-tional chelator S-Acetly-NH3-MAG3.The MIBI was labeled with 99mTc by following the kit instruc-tion.The mice of tumor group were intravenously injected 1-2 mCi of 99mTc-YIGSR or 99mTc-MIBI via caudal vein,immobilized and imaged under a Gamma camera.The same procedure was per-formed in mice of blockade group,in which the unlabeled YIGSR was previously injected to block the receptor-recognition sites,and inflammation group serving as control.The reverse-phase Sep-Pak C18 chromatogram was found to have an essentially complete conjugation between YIGSR and S-Acetly-NH3-MAG3.The conjugated YIGSR could be radio-labeled successfully with 99mTc at room temperature and neutral pH,with a radio-labeling yield of 62%.Without the chelator S-Acetly-NH3-MAG3,the YIGSR was labeled with 99mTc at an efficiency of 4%.The imagological study revealed obvious tumor accumulation of 99mTc-YIGSR 15 min after the injection,and the up-take peaked after 3 h with a tumor-to-muscle ratio(T/M) of 11.36.The radio-tracer was slowly cleared up and resulted in a T/M of 3.01 at the 8th h after the injection.As for blocked group,the tu-mor uptake of radiotracer was significantly lower,with the highest T/M being 4.61 after 3 h and 0.89 after 8 h.The T/M was 3.72 at the 3rd h and 1.29 at the 8th h after the 99mTc-YIGSR injection in the inflammatory group.The T/M was significantly higher in tumor group than in inflammatory group or control group(P<0.001).In the 99mTc-MIBI group,the T/M was 1.40 at the 3rd h and 0.55 at the 8th h after the injection,which showed a significant difference as compared with 99mTc-YIGSR(P<0.001).It is concluded that YIGSR can be successfully radiolabelled by using S-Acetly-NH3-MAG3.99mTc-YIGSR has many advantages in tumor imaging,such as quick and clear visualization,high sensitivity and specificity,and satisfactory target/non-target ratio(N/NT).It promises to be tumor ra-dio-tracer. The validity of 99mTc-YIGSR, a novel receptor radio-tracer, in imaging the Ehrlich ascites tumor was evaluated. YIGSR, a pentapeptide of laminin, was labeled with 99mTc by using a bifunc- tional chelator S-Acetly-NH3-MAG3. MIBI was labeled with 99mTc by following the kit instruc- tion. The mice of tumor group were intravenously injected 1-2 mCi of 99mTc-YIGSR or 99mTc-MIBI via caudal vein, immobilized and imaged under a Gamma camera. The same procedure was per -formed in mice of blockade group, in which the unlabeled YIGSR was previously injected to block the receptor-recognition sites, and inflammation group serving as control. The reverse-phase Sep-Pak C18 chromatogram was found to have an essentially complete conjugation between YIGSR and S-Acetly-NH3-MAG3. The YIGSR could be radio-labeled successfully with 99mTc at room temperature and neutral pH with a radio-labeling yield of 62% .Without the chelator S-Acetly-NH3-MAG3, the YIGSR was labeled with 99mTc at an efficiency of 4%. imag The neural study revealed a significant tumor accumulation of 99mTc-YIGSR for 15 min after the injection, and the up-take peaked after 3 h with a tumor-to-muscle ratio (T / M) of 11.36. The radio-tracer was slowly cleared up and resulted in a T / M of 3.01 at the 8th h after the injection. As for the blocked group, the tu-mor uptake of the radiotracer was significantly lower, with the highest T / M being 4.61 after 3 h and 0.89 after 8 h. T / M was 3.72 at the 3rd h and 1.29 at the 8th h after the 99mTc-YIGSR injection in the inflammatory group. The T / M was significantly higher in the tumor group than in the inflammatory group or control group (P <0.001) .In the 99mTc-MIBI group, the T / M was 1.40 at the 3rd h and 0.55 at the 8th h after the injection, which showed a significant difference as compared with 99mTc-YIGSR (P <0.001). It is that that YIGSR can be successfully radiolabelled by using S-Acetly-NH3-MAG3.99mTc-YIGSR has many advantages in tumor imaging, such as quick and clear visualization, high sensitivity and specificity, and satisfactory target / non-target ratio (N / NT). It promises to be tumor ra-dio-tracer.