Abstract: This invention discloses a method for preparing a therapeutic or diagnostic complex comprised of a nucleic acid ligand and a lipophilic compound or non-immunogenic, high molecular weight compound by identifying a nucleic acid ligand by SELEX methodology and associating the nucleic acid ligand with a lipophilic compound or a non-immunogenic, high molecular weight compound. The invention further discloses complexes comprising one or more nucleic acid ligands in association with a lipophilic compound or non-immunogenic, high molecular weight compound.