The addition of iron, either as Fe dextran or FeCl3, to leukocyte tissue culture medium (containing 20% fetal calf serum) significantly increased the cellular accumulation of subsequently added 67Ga-citrate. This effect of iron was dose-related and decreased, after the initial increase, with increasing concentrations of elemental iron. There was a significant negative correlation (P less than 0.025) between the concentrations of gallium and iron in the medium indicating competition between the two elements for the same serum binding sites. Although it is not yet justified to begin clinical trials, these experiments suggest the possibility that prior administration of iron may increase the usefulness of 67Ga scanning for the diagnosis of neoplasms or abscesses. Further testing of this hypothesis in animals with such lesions would seem indicated.