The present invention concerns methods and compositions for forming PEGylated complexes of defined stoichiometry and structure. In preferred embodiments, the PEGylated complex is formed using dock-and-lock technology, by attaching a therapeutic agent to a DDD sequence and attaching a PEG moiety to an AD sequence and allowing the DDD sequence to bind to the AD sequence in a 2:1 stoichiometry, to form PEGylated complexes with two target agents and one PEG moiety. In alternative embodiments, the target agent may be attached to the AD sequence and the PEG to the DDD sequence to form PEGylated complexes with two PEG moieties and one target agent. In more preferred embodiments, the target agent may comprise any peptide or protein of physiologic or therapeutic activity. The PEGylated complexes exhibit a significantly slower rate of clearance when injected into a subject and are of use for treatment of a wide variety of diseases.