The reliability of the quantitative RT-PCR was estimated by adding total RNA from a normal thyroid to that from 10 ml of blood of a healthy subject. The TG/GAPDH mRNA ratio in the sample without the addition of thyroid RNA was 6.75 × 10 -5 . As the thyroid RNA was increased from 10 ng per 1 l blood to 10 µg per 1 l blood, a linear increase in the TG/GAPDH mRNA ratio was observed, indicating the reliability of this quantitative measurement ( Figure 2) . These results were used in the construction of the standard curve in the following experiments.