T1-201 and I-131 scintigraphy were performed to visualize malignant lesions postoperatively in 26 patients with well-differentiated thyroid cancer. Anyone of uptake index and retention index was higher in malignant lesions than that in benign lesions. T1-201 scintigraphy showed uptake ininflammatory tissues. T1-201 concentration was observed in fourteen patients and six of them had malignant lesions, while I-131 concentration was observed in six patients and all had malignant lesions. In sensitivity, combination of T1-201 and I-131 scintigraphy is higher than I-131 or T1-201 scintigraphy only. In postoperative patients with well-differentiated thyroid cancer, it may be useful that T1-201 scintigraphy will be performed simultaneously with I-131 scintigraphy for detecting recurrence.