1 Introduction.- 2 Clinical Aspects.- 2.1 Occurrence.- 2.2 Clinical Features at Presentation.- 2.2.1 Age and Sex Distribution.- 2.2.2 Symptoms and Signs.- 2.3 Haematology at Presentation.- 2.3.1 Peripheral Blood.- 2.3.2 Bone Marrow Aspiration.- 2.4 Other Investigations.- 2.4.1 Blood Chemistry.- 2.4.2 Serum Proteins.- 2.4.3 Erythrocyte Sedimentation Rate (ESR).- 2.4.4 Radiology.- 2.5 Treatment.- 2.5.1 Splenectomy.- 2.5.2 Chemotherapy.- 2.5.3 Irradiation.- 2.6 Clinical and Haematological Progress.- 2.6.1 Survival and Prognostic Features.- 2.6.2 Course and Fluctuations in the Disease.- 2.7 Complications and Cause of Death.- 2.7.1 Infections.- 2.7.2 Noninfectious Complications.- 3 Pathology.- 3.1 Bone Marrow.- 3.2 Spleen.- 3.3 Liver.- 3.4 Lymph Nodes.- 4 The Hairy Cell: Cytological Aspects.- 4.1 Cytology.- 4.2 Cytochemistry.- 4.2.1 Acid Phosphatase.- 4.2.2 Esterase.- 4.2.3 Periodic Acid-Schiff (PAS).- 4.2.4 ?-Glucuronidase.- 4.2.5 Other Cytochemical Methods.- 4.2.6 Terminal Deoxynucleotidyl Transferase (TdT).- 4.3 Ultrastructure.- 4.3.1 Transmission Electron Microscopy (TEM).- 4.3.2 Scanning Electron Microscopy (SEM).- 4.4 Cytokinetics.- 4.5 Cytogenetics.- 4.6 Metabolism.- 4.7 Culture.- 5 The Hairy Cell: Immunological Aspects.- 5.1 Transformation and Cytotoxicity Studies.- 5.1.1 Mitogen-Induced Transformation.- 5.1.2 Mixed Lymphocyte Reactions (MLR).- 5.1.3 Cytotoxicity Functions.- 5.2 Surface Receptors.- 5.2.1 Sheep Erythrocyte (E) Rosettes and Anti-T Cell Sera.- 5.2.2 Surface Immunoglobulin (Sig).- 5.2.3 Fc Receptors.- 5.2.4 Receptors for Fixed C3 and the Epstein-Barr Virus.- 5.2.5 Receptors for Mouse Erythrocytes.- 5.2.6 Other Markers.- 5.3 Monocytic Features.- 5.3.1 Morphological Aspects.- 5.3.2 Adhesive Properties and Phagocytosis.- 5.3.3 ?Fc Receptors and the la Antigen.- 5.3.4 Monocytopenia and Reticuloendothelial Distribution.- 5.4 Immunoglobulin Synthesis and Secretion.- 5.4.1 Immunoglobulin Secretion.- 5.4.2 Cytoplasmic Immunoglobulin.- 5.4.3 Paraproteinaemia.- 5.5 Summary of the Immunological Membrane Phenotype of Typical HCs.- 5.6 T-cell Features.- 6 Other Haemic Cells.- 6.1 Granulocytes.- 6.1.1 Neutrophils.- 6.1.2 Eosinophils and Basophils.- 6.2 Monocytes.- 6.3 Platelets.- 6.4 Lymphocytes.- 6.4.1 T Cells.- 6.4.2 B Cells.- 7 Diagnosis.- 7.1 Differential Diagnosis.- 7.2 A New Distinct Entity.- 8 Conclusions and Future Trends.- 9 References.- 10 Subject Index.