An ultrastructural study of the action of peptidoglycans on malignant lymphocytes was made. Glycans acted upon lysosomes labilizing and rupturing the lysosomal membrane. Lysosomal enzymes were discharged directly into the cell cytoplasm. Nucleus, mitochondria and all organelles were digested in situ, resulting in a completely structureless cell. Finally, cancerous cells disintegrated by the detachment of cytoplasmic fragments.