Investigation with $^{57}Co-Bleomycin$ in patients with the various cancers and in tumor bearing animals are descirbed. In the patients, $^{57}Co-Bleomycin$ appears to be one of the useful tumor-seeking radiopharmaceuticals, and worth applicable to clinical uses. Labelled yield of $^{57}Co-Bleo$ was about 97 % by thin layer chromatography. The pyrogen free tests were performed to meet U.S.P. critical ranges. In clinical studies with $^{57}Co-Bleo$, 4 cases out of 5 patients with lung cancer., 2 cases among 3 thyroid cancer patients, and all 3 hepatoma patients showed positive tumor scans. The patients with stomach cancer, and the esophageal cancer showed false negative scintigraphy. A case with pulmonary tuberculosis showed a positive scan while liver abscess showed a negative picture. The merits of $^{57}Co-Bleomycin$ scintigraphy seems to be its relatively high affinity to tumors and low radiation hazard in spite of long physical half life.