Radioactive iodine is released at every atomic-bomb testings and nuclear plants accidents and radioactive iodine is taken up by thyroid glands (internal radiation). In addition to the internal radiation, radioactive fallout causes the external radiation and thyroid glands are known to be sensitive to the external radiation. Furthermore, patients with radiation-induced thyroid disease can survive for a long time regardless of the treatment. The survey of thyroid diseases, therefore, is very sensitive and reliable ways to investigate the effects of radiation caused by atomic bomb explosion, testing and various types of nuclear plants' accidents. Our group from Nagasaki University was asked investigate the thyroid diseases and joined to the Sasakawa Project. In order to investigate the effects of radiation on thyroid disease, it is essential 1) to make a correct diagnosis in each subject, 2) to calculate a correct radiation dose in each subject and finally, 3) to find out the correlation between the radiation dose and thyroid diseases including age-, sex- and area-matched controls. We have established 5 centers (1 in Russia, 2 in Belarus, 2 in Ukraine) and supplied the most valuable ultrasonography instruments, commercial kits for the determination of serum free T4 and TSH level and for the autoantibodies, instrument for urinary iodine measurements, syringes, tubes, refrigerators, etc. We visit each center often and asked peoples at centers to come to Japan for training. Protocol of investigation is essentially the same as that in Nagasaki, and we are planning to investigate more than 50,000 children within 5 years. We are hoping to show a definite conclusion in the near future.(ABSTRACT TRUNCATED AT 250 WORDS)