Purpose : The purpose of our study was to assess the usefulness of the Tl-201 SPECT for the detection of the postoperative tumor recurrence on chest wall. Methods: 28 patients including 14 with suspected recurrence of tumor in the chest wall on postoperative chest cr scan, 10 with postoperative pleural effusion which proved benign on radiologic, cytologic and laboratory findings, and 4 with chronic tuberculous empyema as control group were included. All patients underwent SPECT 30 minutes and 4 hours after intravenous injection of 111MBq of Tl-201. Tumor uptake was visually graded by two interpreters and scored as follows : no uptake:0, similar to contralateral lung: 1, higher than contralateral lung but less than heart:2 and similar to heart:3. Results : Markedly increased (grade 3 or 2) Tl-201 uptake was noted in patients with suspected recurrence of tumor in the chest wall (13/14) whereas no (8/10) or minimal (2/10) uptake along the collapsed lung in patients with postoperative benign pleural effusion. In two patients, Tl-201 SPECT revealed additional recurrent tumor mass lesions that were barely perceptible on chest cr scan. Patients with chronic tuberculous empyema showed relatively smoothly marginated increased uptake along the chest wall 4/4), but lesser in degree (grade 1 or 2), when compared to recurrent tumor uptake. Conclusion : Tl-201 lung SPECT seems to be useful to detect postoperative tumor recurrence on chest wall and to differentiate malignant from benign pleural effusion and may provide additional information to the morphologic data obtained by CT.