Recent developments in the field of cellular pathology and molecular biology have had a major impact on our ability to diagnose lymphoreticular disease and on our understanding of many of the disease processes which contribute to lymphoreticular pathology. Twenty years ago, the immunological analysis of lymphoid proliferations was in its infancy. The techniques available, such as sheep red blood cell rosetting and immune adherence to frozen sections, now appear unbelievably crude when compared with our ability to accurately phenotype lymphocytes in suspension, in frozen section and, more recently, in formalin-fixed, paraffin-embedded tissue biopsies. Four international work­ shops have also standardized the nomenclature for the wide range of lineage­ restricted and lineage-related monoclonal antibodies available, and have provided a basis for the sophisticated phenotypic analysis of lymphoid neoplasms in even the smallest routine laboratories. Our concepts relating to the pathogenesis of a number of human lymphomas have also changed substantially, and this has been aided by the development of systems for the classification of human lymphoma which are firmly based in our knowledge of the differentiation and biological behaviour of normal lymphoreticular cells. In this monograph, we present contributions from many authors examining both leukaemia and lymphoma from an immunological perspec­ tive. It is our hope that some of these contributions will be of practical value in the laboratory investigation and diagnosis of lymphoreticular disease. Other contributions record our conceptual understanding of the histogenesis and pathogenesis of human lymphoma.