Gallium-67 concentrates in a variety of soft-tissue and tumor, however the accumulation is not specific for malignant tumor. The increase the tumor to non-tumor ratio is important to improve the quality of the tumor image. It has been recently found that the clearance of 67Ga from blood and the attainment of high ratios of the tumor to normal soft-tissue concentrations are accelerated, if the serum iron concentration is high. The present investigation was, therefore, undertaken in order to study the effect of administered iron after injection of 67Ga on the accumulation of 67Ga in the tumor tissue of mice bearing Ehrlich's ascited tumor. The following results were obtained. The accumulations of 67Ga in the tumor and soft-tissues were slightly decreased compared with controls after ferric acid saccharated (Fesin) administration 3, 6 and 24 hours after injection of 67Ga. However, the tumor to blood ratio (T/B) in each group treated with Fesin was considerably increased because the clearance of 67Ga from the blood is accelerated. The large tumor to blood ratio (T/B) would be advantageous for tumor scanning.