Biolgic distribution of 99mTc-labeled fibrinolytic agent, urokinase, and 99mTc-labeled mannitol, which was obtained as a side-product in the preparation of 99mTc(Sn)-urokinase, have been studied in Ehrlich's tumor-bearing mice to get a promising indicator for the positive delineation of malignant tumor. The preparation of 99mTc-labeled radiopharmaceuticals, 99mTc-UK and 99mTc-Man, was made by the reduction with stannous chloride and labeling efficiency was examined by Sephadex G-25M gel chromatography and by silica gel plate thin layer chromatography. Labeling yield of 99mTc-UK by Sephadex G25M in 0.9% NaCl eluant was 13% and that of 99mTc-Man by TLC in 85% methanol solvent was over 95%. A higher uptake to the implanted solid tumor tissue in mice was found in 99mTc-Man than in 99mTc-UK, of which the excellent tumor accumulation was expected from the positive delineation of malignant tumor with 131I-fibrinogen, 131I-fibrinogen antibody and 125I-plasmin. The poor result in 99mTc-UK, however, may be attributed to the poor fibrinolytic activity of Ehrlich's tumor. In biologic distribution of 99mTc-UK was found high concentration for liver kidney and stomach. In the other hand, a higher tumor tissue uptake, a fast blood disappearance and a low concentration for different organs were found in biologic distribution of 99mTc-Man. Therefore, 99mTc-Man may be assumed as a more preferable 99mTc-labeled tumor localizing radiopharmaceuticals, to which it would be needed as absolute biologic characteristics that 99mTc-labeled compounds possess a high tumor uptake as well as a fast blood disappearance with a low uptake for different organs. However, the possible delineation with 99mTc-labeled fibrinolytic agents, including urokinase and streptokinase, may be promised for malignant tumors in human-subject, which generally have a higher activity in fibrinogenesis than in fibrinolysis.