1 Biochemical, Immunological, and Molecular Markers of Hemopoietic Precursor Cells.- 1. Introduction.- 2. Biochemical Markers.- 2.1. Terminal Deoxynucleotide Transferase.- 2.2. Enzymes in Nucleotide Metabolism.- 3. Immunological Markers.- 4. Molecular Markers.- 5. Analysis of Human Hemopoietic Ontogenesis by Immunological and Molecular Markers.- 6. New Opportunities for Immunological and Molecular Markers: Minimal Residual Disease Detection and Therapeutical Approaches.- 7. References.- 2 Cell Surface Markers in Leukemia and Lymphoma.- 1. Introduction.- 2. B Cells.- 2.1. Normal B-Cell Ontogeny.- 2.2. B-Cell Leukemias and Lymphomas.- 3. T Cells.- 3.1. Normal T-Cell Ontogeny.- 3.2. T-Cell Leukemias and Lymphomas.- 4. Myeloid Cells.- 4.1. Normal Myeloid Ontogeny.- 4.2. Myeloid Leukemias.- 5. Summary.- 6. References.- 3 Cytoskeletal Organization of Normal and Leukemic Lymphocytes and Lymphoblasts.- 1. Introduction.- 2. Microfilaments in Normal and Leukemic Lymphocytes and Lymphoblasts.- 2.1. Actin and Actin-Associated Proteins in Nonmuscle Cells.- 2.2. Actin Isoforms.- 2.3. Organization of Actin in Normal Lymphocytes.- 2.4. Interactions between Actin and Surface Antigens in Lymphocytes.- 2.5. Actin in Leukemic Lymphocytes and Lymphoblasts.- 3. Intermediate-Size Filaments in Normal and Leukemic Lymphocytes and Lymphoblasts.- 3.1. The Intermediate Filament System.- 3.2. Distribution of Vimentin in Lymphocytes in Normal Conditions.- 3.3. Vimentin in Neoplastic Lymphocytes and Lymphoblasts.- 3.4. Expression of Cytokeratin in Lymphoid Tissues.- 4. Microtubules in Lymphoid Cells.- 5. Organization of Spectrin in Lymphocytes.- 6. Conclusions.- 7. References.- 4 Signaling Events in T-Lymphocyte-Dependent B-Lymphocyte Activation.- 1. Introduction.- 2. B-Cell Antigen Receptor-Mediated Signaling.- 3. Molecular Bases of T-Cell-Mediated B-Cell Signaling.- 4. Biological Evidence for Ia-Mediated Signal Transduction.- 5. Biochemical Evidence for Ia-Mediated Signal Transduction.- 6. Conclc'