Targeting of imaging probes specifically to diseased tissues such as cancer is attractive because it potentially allows the improvement of tumor detection. One of the problems associated with conventional, low molecular weight imaging probes is the limited tumor:background ratio. To circumvent this, imaging probes may be conjugated to polymeric carriers to target solid tumors by either passive accumulation of macromolecules into tumor tissues due to the “enhanced permeability and retention” effect (EPR effect) or active targeting through the incorporation of cell-specific recognition ligands that mediate binding to cancer-specific antigens. This invention describes an innovative targeting strategy for the selective delivery of diagnostic agents into solid tumors by means of polymer-NIR fluorochrome conjugates modified with targeting ligands that bind to antigens or receptors that are uniquely expressed or over-expressed on the target cells relative to normal tissues.