The effects of glycolipids on the interaction of the MIF (migration inhibition factor) with rat macrophages were examined using a migration inhibition assay system. MIF activity was specifically blocked by fucosylated Glycolipid RM [Galα1-3Gal(2-lαFuc)β1-3GalNAcβ1-3Galβ1-4Glcβ1-1ceramide, (1978) J. Biochem. 83, 85–90], but not by Cytolipin R, hematoside, or blood group B active glycolipid [Galα1-3Gal(2-1αFuc)β1-4GlcNAcβ1-3Galβ1-4Glcβ1-1ceramide]. Inhibition of MIF activity was proportional to the concentration of Glycolipid RM. These findings suggest that Glycolipid RM acts as a receptor for MIF.