Using this method, the expression levels of TG mRNA in the peripheral blood of 57 patients and 17 healthy subjects were calculated. All the samples were successfully measured by real-time quantitative RT-PCR, which confirmed the expression of TG mRNA in all the samples. There was no statistical difference between the patients with and without metastasis (Figure 3 ). The serum TG was measured in the 49 DTC patients without serum anti-TG antibody, and the set of results were compared (Figure 4) . No statistical differences in the TG mRNA levels were observed. While serum TG was detectable in all the patients with metastasis, it was undetectable in 14 of 29 patients without metastasis. Further, serum TG was undetectable in all 4 patients diagnosed with medullary carcinoma, while quantitative measurement of TG mRNA was possible (Figure 3) . These results suggest that serum TG is a superior marker of distant metastasis of DTC than TG mRNA in peripheral blood. Further, the correlation between TG mRNA and serum TG was estimated in these 49 patients and no correlation was observed between the two ( Figure 5 ).