Whether the problems encountered with oral administration of soluble protein antigens can be overcome by the use of improved mucosal adjuvants [muranyl dipeptide, immune stimulating complexes (ISCOMs), cholera or Escherichia coli enterotoxins, avridine, proteosomes, cytokines, etc.] or new and novel delivery systems (liposomes, live recombinant vectors, microspheres, DNA plasmids, virus-like particles) requires further investigation, and specific examples are given in this review.