Neither a preinjection of nonlabeled H7 nor a postinjection of alpha H7 nor a combination of both strategies resulted in improved tumor/nontumor dose ratios compared to a single injection of labeled H7. The monoclonal antibody H7 has a rapid and high uptake, combined with a prolonged retention time in the tumors. The kinetic properties of H7 are different from antibodies targeting intracellular tumor antigens.