67Ga citrate was used to investigate mechanisms of tumor scanning in rabbits. Both carcinoma and streptococcal abscesses absorbed 67Ga and were visualized on the scans. 67Ga was found to be bound to the protein fraction of the serum. More radioactivity was seen in the soluble fractions of the tumor cells. 67Ga may be carried to tumor cells by the serum protein, taken up rather specifically by tumor cells in a manner which is still unknown, and retained there for some time. Inflammation around the tumor and increased vasculature in the neoplasm may also be significant.