The present invention concerns methods and compositions for PEGylated complexes of defined stoichiometry and structure. Preferably, the PEGylated complex is formed using dock-and-lock technology, by attaching a therapeutic agent to a DDD sequence and a PEG moiety to an AD sequence, allowing the DDD sequence to bind to the AD sequence in a 2:1 stoichiometry, to form PEGylated complexes with two therapeutic agents and one PEG moiety. Alternatively, the therapeutic 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 therapeutic agent. In more preferred embodiments, the therapeutic agent may comprise any peptide or protein of physiologic or therapeutic activity, preferably a cytokine, more preferably interferon-α2b. 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.