BACKGROUND: It is known that 99mTc-MIBI(technetium-99m methoxyisobutyl isonitrile), a lipophilic cation is uptaked by myocardium or neoplastic cells but not by normal cells. There have been several reports which studied the significanes of 99mTc-MIBI in the differential diagnosis of solitary pulmonary nodules. SUBJECTS AND METHODS: Author conducted a study on 10 consecutive cases of benign pulmonary nodules (BPN; tuberculosis 6, others 4) and 14 cases of lung cancer (small cell cancer). One and 4 hour after injecting 740 MBq of 99mTc-MIBI, planar and SPECT images were obtained. Tumor 99mTc-MIBI uptake was expressed as PTL (planar tumor to normal lung ratio) and STH (SPECT tumor to heart ratio). RESULTS: On planar and SPECT images 99mTc-MIBI uptake was prominent in lung cancer, while no definitive uptake was observed in BPN. PTL, PTH,, STL and STH of 1 hour after 99mTc-MIBI injection were significantly higher in lung cancer group compared to BPN while those of 4 hour were not significant between them. In lung cancer group, STH of 4 hour images were significantly decreased compared to 1 hour images, while no difference was observed in BPN. In the differential diagnosis of lung cancer and BPN, using PTL (with cut-off value 1.2), sensitivity was 78% and the specificity was 79%. CONCLUSION: It is suggested that 99mTc-MIBI uptake ratio and clearance could be used for the differential diagnosis of lung cancer and BPN.