Previously, we reported that the deposition of 67Ga into malignant tumors may be a sensitive index of proliferative activity in tumor cells. For the purpose of elucidation of this hypothesis, we investigated the relationship between the accumulation of 67Ga into malignant tumor cells and the intra cellular ATP metabolism in vitro. The uptake of 67Ga into tumor cells was inhibited by adding NaF which is an inhibitor of ATP production. Furthermore, the uptake of 67Ga into tumor cells was strongly inhibited by adding ouabain which is a specific inhibitor of Na+-K+-ATPase. From these in vitro results, it was concluded that there is a correlation between 67Ga uptake and intra cellular ATP metabolism in tumor cells.