Hemopoietic Microenvironments Historical Perspectives, Status, and Projections.- Historical Perspectives, Status, and Projections.- Definition.- Radiation Protection by Marrow Transplantation.- The Spleen Colony Assay.- Antecedents of the Hemopoietic Microenvironment Concept.- Spleen Colony Types.- Spleen Colony Retransplantation.- Effect of Erythropoietin Deprivation on Spleen Colony Types.- Visualization of Erythropoietin-Sensitive Stem Cell Colonies.- Decision for Lineage-Specific Differentiation.- Endoclonal Origin of the Second Line of Differentiation.- The Working Hypothesis.- Tests of the Working Hypothesis.- Microenvironmental Control of Mast Cell Differentiation.- Dissecting the Hemopoietic Microenvironment.- Other Evidence of the Roles of Marrow, Spleen, and Thymus Organ Stroma in Hemopoiesis and Lymphopoiesis.- Hemopoiesis on Intraperitoneal Cellulose Acetate Membranes.- CFU-S Heterogeneity.- Reversible Effect of Marrow and Spleen Microenvironments on Thymic Progenitor Cell Differentiation and Proliferation.- Reversible Predisposition of CFU-S for Direction of Differentiation.- Hemopoietic Hormone (Growth Factor) Receptors.- Pluripotency of Hemopoietic CFU-S for Lymphoid Differentiation.- Lymphoid-Inductive Microenvironments.- In Vitro Bone Marrow Cultures.- Distinctive Stromal Cells of Erythroid and Granuloid Spleen Colonies.- Other Candidate for In Vivo Hemopoietic Microenvironment Stromal Cells.- Hemopoiesis.- Projections.- Malignancy-Inducing Microenvironments?.- References.- Molecular and Cellular Traffic Across the Marrow Sinuses.- Marrow Structure.- Evidence for Discrimination in the Release of Marrow Cells.- Factors Governing Release of Hemopoietic Cells.- Cell Releasing Factors.- The Anatomical Process of Release.- Release from and Reentry into Marrow of Stem Cells and Progenitor Cells.- References.- In Vivo Microscopy of Hemopoietic Tissue.- In Vivo Microscopic Methods.- In Vivo Microscopic Studies of Hemopoietic Tissue.- References.- Fatty Involution of Marrow and the Role of Adipose Tissue in Hemopoiesis.- Distribution of Red and Yellow Marrow.- The Role of Bone.- Ectopic Implantation of Bone Marrow.- Marrow Adipocyte.- Distinct from Extramedullary Adipocytes.- Heterogeneity of Marrow Adipocytes.- Marrow Adipocytes in Culture.- Conclusions.- References.- Hematopoiesis on Artificial Membranes.- Hematopoiesis on Flat CEM.- Hematopoiesis On Stromally-Enriched, IP-Implanted Tubular CEM.- Hematopoiesis and Proteoglycans.- Role of Bone and Tooth Matrix Proteins in Hematopoiesis.- Irradiation of Stromal Cells.- Studies of Scraped, Devitalized, and Reimplanted CEM.- Overall Perspective and Significance of Hematopoiesis on CEM.- References.- Cellular Components of Stroma In Vivo in Comparison with In Vitro Systems.- Cellular Components of the Stroma.- References.- Stromal Cells in Long-Term Bone Marrow Cultures.- Cell Types in Adherent Layer.- Growth Factor Production by Adherent Cells.- Studies in Other Species Including Human.- Lymphoid Growth and Long-Term Culture.- TC-1 Cell Line.- Hypothesis.- References.- Cultured Stromal Cell Lines from Hemopoietic Tissues.- The Hemopoietic Microenvironment.- Hemopoietic Stromal Cell Lines.- Summary.- References.- Cellular Interactions in the Regulation of Human Hemopoiesis In Vitro.- Normal Hemopoiesis.- Abnormal Hemopoiesis.- References.- The Collagenous Hemopoietic Microenvironment.- The Genetically-Distinct Types of Collagen.- Collagenous Bone Marrow Stroma.- Synthesis of Collagenous Matrix by Stromal Cells of the Bone Marrow.- Bone Marrow Collagen in Hematologic Disorders.- Myelofibrosis.- Future Prospects.- References.- The Hemopoietic Extracellular Matrix.- The Role of the Extracellular Matrix in Regulating Cell Growth and Differentiation.- Characterization of Noncollagenous Extracellular Matrix Macromolecules Found in Bone and Bone Marrow.- Identification of Extracellular Matrix Proteins in the Stroma of Long-Term Bone Marrow Cell Cultures.- The Role of Extracellular Matrix Components in Regulating Hemopoiesis in Long-Term Bone Marrow Cultures.- Reconstitution of Bone and Bone Marrow In Vivo by Ectopic Implantation of Devitalized, DemineralizedBone Matrix.- Studies of the Abnormal Hemopoietic Microenvironment of Sl/Sld Mice.- Summary.- References.- Bone Marrow Microenvironment Clinical Observations.- Clinical Implications.- Functional Abnormalities of Cellular Components of Bone Marrow Microenvironment.- References.