After almost two decades of research, evidence suggests that transferrin receptors are rate-limiting in 67Ga uptake, 67Ga imaging is an in vivo detector of transferring receptors and an indicator of tumor cell proliferation. Moreover, 67Ga can be incorporated into tumor cells by a transferrin receptor-independent process. This pathway could be important in patients with saturated transferrin. Data that appear to support the concept that transferrin receptor-independent transporters are rate-limiting can be resolved by considering the presence of the gallate ion, [67Ga (OH)4]-.