An in vivo method for delivering a diagnostic or therapeutic agent to a target site in a mammal, wherein a targeting species including a targeting moiety and a diagnostic or therapeutic agent or a binding site for a subsequently administered diagnostic or therapeutic agent conjugate, the targeting moiety having a primary binding site whereby it specifically binds to the target, is administered and allowed to accrete at the target site, is improved by injecting into the circulatory system of the mammal a clearing agent that binds to the primary binding site of the targeting species, whereby non-localized primary targeting species is cleared from circulation. The method is especially useful in pretargeting methods because the clearing agent does not remove the primary targeting species or block secondary binding sites of the primary targeting species.