In contrast to the immunosuppressive effects of C2-ceramide (C2-Cer), alpha-galactosylceramides with ceramides having more than 10 carbons in fatty acid chains have immunostimulatory activities. We therefore synthesized alpha- and beta-galactosylated C2-Cers in order to examine their effects on the immune system. beta-Galactosylated C2-Cer and C2-Cer suppressed the allogeneic mixed leukocyte reaction (MLR) responses, but alpha-galactosylated C2-Cer stimulated the MLR response.