Abstract Human melanoma cells were incubated with 67Ga-citrate, a mixture of 67Ga-citrate and transferrin, 67Ga-transferrin and 67Ga-transferrin- 125I. It was found that there was a greater and more rapid uptake of 67Ga by the tumor cells when the gallium was complexed to transferrin. It was further noted that when melanoma cells were incubated with 67Ga-transferrin- 125I, the 125I associated with the cell fraction remained constant after 15 min of incubation while the 67Ga associated with the melanoma cell fraction continued to increase beyond this point. Experiments have indicated the presence of both a passive and active mechanism for the uptake of radiogallium by the human tumor cells. However, it appears that passive diffusion did not play the major role in such uptake and that the transport of 67Ga into the tumor cells was mediated solely through transferrin of the serum proteins studied. It is further suggested that 67Ga enters the cell after the gallium-transferrin complex combines with a cell surface receptor and that pinocytosis does not play a role in the uptake of 67Ga by the tumor cell.