Abstract: The present invention provides IgG monoclonal antibodies and IgG monoclonal antibody fragments that selectively bind to PEG, hybridoma cell lines and methods for producing these antibodies, and methods for using the PEG-selective monoclonal antibodies. The methods of the invention include methods for detecting molecules, viruses, cells, or organelles that contain at least one poly(ethylene glycol) group and methods for purifying for purifying molecules, viruses, cells, or organelles that contain at least one poly(ethylene glycol) group. Also provided are methods for using the anti-PEG monoclonal antibodies in vivo to modulate the level of a PEG-containing molecule.