7 laboratories located in Seoul were surveyed for the standardization of radioiodine thyroid uptake test in Korea. The result revealed that the currently utilized methods are almost standardized now, when the reference standard is IAEA recommendation method, 1962. Mean 24 hour uptake of thyroidal 131I in Korean euthyroids is 31.6¡¾8.80%, and no significant interlaboratory differences are noticed. These results were caused probably by the late introduction of detector facilities into Korea after the appearance of publication of IAEA recommendations.