Protein and peptide therapeutics currently represent eight of the top 100 prescription pharmaceuticals in the U.S., and biotechnology products are projected to account for 15% of the total US. prescription drug market by 2003. Of the protein and peptide products now on the market, many are administered as daily injections, though several are deliveredby noninvasive routes. For example, desmopressin is delivered as a nasal spray, and deoxyribonuclease I is administered by inhalation. Although cyclosporin A is orally active, as yet there are no general means to confer oral bioava- ability to...