Technetium-99m-tetrofosmin is a new myocardial imaging agent which has yielded promising results compared to thallium-201. The tumour-seeking properties of the routinely used cardiac radiopharmaceuticals201Tl and99mTc-methoxyisobutylisonitrile are well known. Here we report the results of a pilot study demonstrating99mTc-tetrofosmin uptake in malignant lung tumours. Five patients with bronchial carcinoma, each in different stages of chemo- or radiotherapy, were imaged. Dynamic and static acquisitions were performed to evaluate the uptake and kinetics of99mTc-tetrofosmin in the lesions. In four of the five patients localized tumour uptake of99mTc-tetrofosmin was observed. Time to peak tumour activity and tracer washout in the tumour, myocardium and contralateral normal lung at 30 min post injection (p.i.) were determined. Tumour/normal lung, heart/tumour and heart/contralateral normal lung ratios were calculated for 5-10, 25-30 and 85-90 min p.i. The peak concentration in all tumours was reached at the end of the first minute. The mean tumour and contralateral normal lung washout rates of99mTc-tetrofosmin at 30 min p.i. were 18.3%±9.2% and 19.5%±5.85% respectively. The tumour/contralateral normal lung ratio remained higher than 1.25 until 90 min p.i. in all four patients. It is concluded that99mTc-tetrofosmin seems to be of value in lung tumour imaging, although larger studies are necessary to ascertain its sensitivity, specificity and usefulness in clinical practice. © 1995 Springer-Verlag.