BACKGROUND: 99mTc MIBI(Methoxyisobutylisonitrile complex), a member of the isonitrile class of coordination compounds, is a lipophilic cation presently under investigation for clinical use as myocardial perfusion imaging agent and is widely used to detect myocardial infarction. Preliminary reports indicate that T1-201 accumulate in human neoplasm and several authors reported 99mTc MIBI may also localized in primary malignant tumor and metastatic deposits from lung cancer. We evaluated the uptake of 99mTc MIBI in lung cancer and localization of mediastinal and other site metastasis, and compared the benign lesion of the lung. METHOD: Thirty four patients of lung cancer and ten patients of benign lung lesion were studied with chest CT and 99mTc MIBI Lung SPECT. 99mTc MIBI uptake ratio was assessed by TR/NL(Lung lesion/ Normal area), HT/NL (Heart/ Normal area) and HT/TR(Heart/Lung lesion). RESULTS: 1) All lung cancer patients showed increased uptakes of 99mTc MIBI in malignant lung lesion and Tc-99m MIBI uptake was also increased in mediastinal and lymph node metastasis except two cases. 2) There was significant different ratio of TR/NL between malignant and benign lesion, 3.79 +/- 1.82 and 1.67+/-0.63 on planar images, respectively(p <0.001). 3) There was no significant difference of 99mTc MIBI uptake ratio between squamous cell carcinoma, small cell carcinoma and adeno carcinoma(3.64+/- 1.66, 3.57+/-0.72, 4.31 +/-2.28 respectively). CONCLUSION: 99mTc MIBI lung SPECT was useful in the localization of tumor and mediastinal or other site metastatic lesion in lung cancer and also in the differential diagnosis between benign and malignant lesion.