The desire to deliver protein and peptide biopharmaceuticals conveniently and effectively has led to intense investigation of site-specific drug-delivery systems. Despite challenges, progress towards the convenient noninvasive delivery of proteins and peptides has been achieved through specific routes of administration. In addition, the delivery of proteins and peptides to specific sites of action has been utilized to lower the total delivered dose, to gain access to specific organs or body compartments and to concentrate a therapeutic dose at a specific site of pharmacological action.