A method and compositions are described for labeling a targeting agent with Ga-68, in which eluate from an acid-eluted Ge-68/Ga-68 generator is combined with a macrocycle-containing targetable agent. The labeling method and compositions disclosed ensure that a simple elution of gallium-68, taken directly from a generator, can be used without further manipulation to quantitatively label a macrocycle-containing targetable agent. The Ga-68 labeled targeting agent so produced is useful with specific targeting agents, and is most especially useful in a pretargeting method for positron emission tomographic detection.