Abstract: Disclosed is a method for reducing an immune response to a parenterally administered non-autologous antigen in an individual who is immunologically responsive thereto by mucosally administering to the individual an amount of the antigen effective to reduce any immune response to parenteral administration of said antigen. The antigen can be a polypeptide such as a hormone, like insulin, which supplements a metabolic deficiency in the recipient of a polypeptide intended to serve the same function. The polypeptide can also be one which supplements a deficiency in the production of a physiologically important polypeptide, such as a hematologic regulatory factor. The hematologic regulatory factor can enhance or inhibit thrombogenesis or platelet deposition. Also, the antigen can be a tissue or cell preparation, such as of allogeneic or xenogeneic tissue or cells.