A glycolipid which was expressed during a differentiation from haploid myxoamoebae to diploid plasmodia of a true slime mold, Physarum polycephalum, has been examined. In the amoeboid stage, cells did not contain this glycolipid, but after conjugation of the haploid cells, this substance appeared and increased in its amount. From structural studies of the purified glycolipid, it has been identified as poriferasterol monoglucoside.