The present invention relates to a conjugate that includes a nucleic acid ligand bound to a controlled release polymer system, a pharmaceutical composition that contains the conjugate, and methods of treatment using the conjugate. The controlled release polymer system includes an agent such as a therapeutic, diagnostic, prognostic, or prophylactic agent. The nucleic acid ligand that is bound to the controlled release polymer system, binds selectively to a target, such as a cell surface antigen, and thereby delivers the controlled release polymer system to the target.