We have labeled surface glycoproteins of normal and malignant human blood leukocytes by the galactose oxidase-NaB3H4 and periodate-NaB3H4 labeling techniques. The labeled glycoproteins were separated by slab gel electrophoresis in the presence of sodium dodecyl sulfate and visualized by fluorography. The different types of normal blood cells could be distinguished by their surface glycoprotein patterns. The surface glycoproteins of cells from patients with acute lymphoblastic, myeloid, or monoblastic leukemia were different from those of normal cells. The leukemic cells could be classified by their surface glycoprotein patterns with respect to their relationships to normal blood cells, and an estimation of their degree of differentiation was obtained.