The distribution of neutral, or asialosyl-, glycosphingolipids and gangliosides in a rhabdomyosarcoma of alveolar type have been studied. Histologically, this muscle tumor is composed primarily of two cell types: one with oval or round hyperchromatic nuclei and very little cytoplasm, and one a giant cell, with multiple, peripherally placed nuclei and weakly staining eosinophillic cytoplasm. In comparing glycolipids of the rhabdomyosarcoma with normal muscle from the same leg, the striking alteration in the tumor was a virtual disappearance of ganglioside GM2. There was also a slight increase in GM3 and a decrease in GD1a. The asialosyl derivative of GM2 (GalNac-Gal-Glc-Cer) was markedly increased in the tumor. A loss of glucosylceramide was also observed. The results are discussed in terms of glycolipid metabolic changes in muscle oncogenesis and their implications.