1) On the rabbits suffering from cobalt-polycythemia iron metabolism was studied in various ways. Blood picture, level of serum iron and serum copper, and mobilization of stored iron showed the same tendency as that observed in recovery from bleeding anemia. Distribution of intravenously injected radioactive iron was also similar to that of bleeding anemia with an exception in which the incorporation of radioactive iron into the liver was greater than into the bone marrow. 2) The influence of cobalt on the uptake and utilization to the heme synthesis of radioactive iron by rabbits bone marrow cells in vitro was studied. The rate of utilization to the heme synthesis was maximal in the ratio of 1 : 100 (Fe : Co) in radioactive iron concentration 20 γ %. However, cobalt had no influence on the iron uptake of bone marrow cells.