Three round-cell sarcomas which involve bone—Ewing's sarcoma, malignant lymphoma, and metastatic neuroblastoma—all show similar morphological cell patterns using routine light microscopic techniques. Glycogen in Ewing's sarcoma cells and reticulin fibers surrounding malignant lymphoma cells of the reticulumcell sarcoma type can be demonstrated by special stains and light microscopy, but with even greater specificity by electron microscopy. Urinary excretion of catecholamine and intermediate metabolites in neuroblastoma is associated with the presence, in cells of this tumor, of neurosecretory granules which can be seen by electron microscopy. Neural processes and junctional complexes further help to distinguish the cells of this tumor from the other round-cell sarcomas.