Complex lipids in eukaryotic membranes include glycerophospholipids and complex sphingolipids. Complex sphingolipids are a collective term for sphingolipids with hydrophilic heads. Complex sphingolipids form lipid microdomains on biological membranes, which are involved in proper localization and exertion of functions of various membrane proteins. In addition, the synthetic intermediates and metabolites of complex sphingolipids, such as ceramides, sphingoid bases, and sphingoid base 1-phosphates function as lipid signaling molecules that regulate intracellular and extracellular signal transduction systems. We are trying to elucidate the physiological functions of sphingolipids, which is often referred to as the "mystery of the sphinx," using budding yeast Saccharomyces cerevisiae, which allows a wide range of molecular genetic approaches.