Bronchial carcinoma is the leading cause of death from cancer in most countries. The aim of this prospective study was to assess the ability of 99mTechnetium Sestamibi (99mTc-MIBI) SPECT in differentiating benign from malignant pulmonary masses. 30 patients with lung mass, radiologically suspicious for malignancy were included. Planar scintigraphy was performed on all patients 10 and 120 min after intravenous injection of 99mTc-MIBI. Also SPECT was done after completion of first static image series. Images were evaluated qualitatively and quantitatively for abnormal accumulation of radiotracer corresponding to the location of the masses. Increased 99mTc-MIBI uptake was considered as positive scan result. Biopsy from lung mass was performed in all patients. Twenty patients (67%) had malignant lung lesions, which were confirmed pathologically [90% had primary lung cancer (PLC)]. 99mTc-MIBI scan had sensitivity, specificity, positive and negative predictive values of 80, 70, 84 and 64% in detection of lung malignancies, respectively. Quantitatively, malignant lesions revealed high mass/lung count ratio comparing to benign lesions (1.21 +/- 0.12 vs. 1.09 +/- 0.07, p<0.01). Small cell tumors had higher 99mTc-MIBI uptake than squamous cell tumors (p<0.05). 99mTc-MIBI scanning can be helpful in prediction of malignancy in suspicious pulmonary masses due to its high specificity and positive predictive value.