Possiblity of differential diagnosis by means of the scintigram of thyroid gland was investigated with 15 cases with chronic inflammation, 54 with benign tumor, 22 with malignant tumor as the subjects of the study. The results are briefly summarized as follows. 1) In chronic inflammatory diseases most cases show an irregularity of the color band, and the lesion site is mostly located in the upper pole followed by the lower pole. 2) In cases of benign tumor warm nodules are decidedly predominant as compared with other diseases, and the margin is mostly either sharp or diffuse, especially sharp one in benign tumor than in malignant one. The peripheral contour is mostly concave. Enlargement of the lesion area is more often observed than in other diseases, and this tendency is especially marked in warm nodule. There can be often observed oppressive deformation. There is no difference of the color level between the right and the left sides. Lesion site does not differ from the right to the left side and it is mostly on the right exterior side and the left lower pole. 3) In malignant tumor, most cases show a large lesion. Ones with irregular margin are more numerous than in other diseases, but here it requires differentiation from inflammation. There is no swelling on the sideof lesion. The oppressive deformity is not so frequent as in benign cases. The affected side in most cases shows a lower color level as compared with healthy side. The lesion site in this case is mostly located in the upper pole.