Kinetics of Tc-99m MIBI uptake was studied in 19 patients with lung lesions (6 benign, 13 malignant). Two dynamic studies were acquired after the I.V. injection of 10-15mCi (370-550 MBq); the first was every second for 60 seconds, followed by a second one every minute for 30 minutes. Delayed images were acquired at two and three hours. By assigning regions of interest (ROI) over the lung lesions (TR), contralateral normal lung (NL) and the heart (Ht), time activity curves (TAC) were generated and time to peak activity was calculated as well as the ratios of TR/NL, Ht/TR and Ht/NL. The Ht/NL ratio was also assessed in five patients referred with diagnosis of ischaemic heart disease (IHD) for myocardial imaging. There was a localized increase of Tc-99m MIBI uptake in ten patients with untreated malignant tumours of the lung. No localized uptake was found in one patient with untreated poorly differentiated squamous cell carcinoma, two treated lung cancer and four patients with non-malignant lesions of the lungs. Two patients with fibrosing alveolitis showed diffuse increase lung uptake. In all positive studies peak tumour was reached within the first minute. There was no statistical difference in the ratio of Ht/NL between all groups except in patients with fibrosing alveolitis. There was no significant difference between the ratios TR/NL, Ht/TR and Ht/NL at 5-10 minutes and 25-30 minutes. The ratio of TR/NL at 25-30 minutes was 1.58 +/- 0.36 in the positive cases versus 1 +/- 0.22 in the negative ones.(ABSTRACT TRUNCATED AT 250 WORDS)