Medicinal compositions which can be processed into solutions and are useful in inhibiting rejection reactions against the transplantation of organs or bone marrow, in the maintenance immunotherapy therefor or in treating autoimmune diseases, characterized by containing 2-amino-2-[2-(4-octylphenyl)ethyl]propane-1,3-diol or pharmaceutically acceptable acid-addition salts thereof and cyclodextrins as a stabilizer optionally together with saccharides, if required.