1. A. Pusztai, Transport of proteins through the membranes of the adult gastro- intestinal tract — a potential for drug delivery? Adv. Drug Deliv. Rev. 3 (1989) 215–228.
2. A. Bernkop-Schnürch and R. Fragner, Investigations into the diffusion behaviour of polypeptides in native intestinal mucus with regard to their peroral administration, Pharm. Sci. 2 (1996) 361–363.
3. J.F. Woodley, Enzymatic barriers for GI peptide and protein delivery, Crit. Rev. Ther. Drug 11 (1994) 61–95.
4. A.F. Bristow, The current status of therapeutic peptides and proteins, in: R.C. Hider and D. Barlow (Eds.), Polypeptide and Protein Drugs — Production, Characterization and Formulation, Ellis Horwood, Chichester, UK, 1991, pp. 54–69.
5. G.J. Russel-Jones and H.J. de Aizpurua, Vitamin B12: a novel carrier for orally presented antigens, Proc. Int. Symp. Control Rel. Bioact. Mater. 15 (1988) 142–143.