We investigated whether sulfatides are able to trigger transmembrane signals and activation of selective cell functions in human monocytes. Sulfatides stimulated an increase in cytosolic free-calcium in monocytes, and this depended on the release of calcium from intracellular stores. Non-sulfated galactocerebrosides had no effect on monocyte cytosolic free calcium. Sulfatides enhanced expression of tumor necrosis factor, interleukin-8, and interleukin-1 beta, but not interleukin-12/natural killer cell stimulating factor mRNAs. Sulfatides also triggered secretion of cytokines into the extracellular medium, although they were much less effective than lipopolysaccharide. Both enhanced expression of cytokine mRNAs and secretion by sulfatides required sulfation of the galactose ring of the glycolipid as non-sulfated galactocerebrosides had no effect. These findings suggest that sulfatides that are released at sites of inflammation can amplify the inflammatory reaction triggering cytokine expression in, and release by, monocytes.